SUMMARY

This article describes the various SMTP return codes that senders may receive when communicating with the SMTP service.

DETAIL

The easiest way to determine why inbound messages are not being processed by the SMTP connector is to examine the SMTP Activity and Debug logs. The logs can be accessed through the administration program, by expanding the Servers->Localhost->Services and Connectors->SMTP->Logs branch. These log files record SMTP transactions and their associated response codes. These response codes are explained further with possible resolutions below:

220 Service ready

Error Description: This response is sent from the SMTP server when a remote SMTP client or host has successfully connected to the SMTP service.

221 Service closing transmission channel

Error Description: This response is sent from the server when the remote server/client has notified that it is closing the connection. You would commonly notice this command after a QUIT command was received.

250 Requested mail action okay, completed

Error Description: This response indicates that a SMTP command was received by the server and successfully processed.

354 Start mail input; end with .

Error Description: This response is sent by the SMTP server and instructs a remote SMTP server or client that the DATA command was accepted and that it can commence sending the actual message.

421 Service not available, closing transmission channel

Error Description: This response is sent by the SMTP server to a remote SMTP server or SMTP client to indicate that the MailEnable SMTP Server is currently unavailable.

Error Resolution: When this error is returned in the logs or to a client then it usually means that the data store in particular the configuration directory data cannot be accessed.
When using a default install of MailEnable you can check and repair the permissions on the MailEnable TAB delimited configuration files by comparing and/or executing the commands in step 6 of the following article:

Reset MailEnable Permissions

If you have changed your default installation to use the MailEnable database provider and are using an SQL database server while getting this error then ensure that the database is online. If the database is online then ensure MailEnable services are able to connect and retrieve data from the database tables you may also find errors for this within the server Event Logs.

451 Requested action aborted: error in processing

Error Description: This response is sent by the SMTP server to a remote SMTP Server or SMTP client to indicate that the MailEnable SMTP Server is currently unable to complete the transaction or command. There can often be more information contained within the SMTP debug logs for this error.

Error Resolution: When this error is returned in the logs or to a client then it usually means that the data store in particular the configuration directory data cannot be accessed. The first thing to check is that your hard drive is not full or faulty or in some cases ensure that any quotas enabled on the drive are not being exceeded. Information on these types of problems can usually be found in the server Event Logs.

When using a default install of MailEnable you can check and repair the permissions on the MailEnable TAB delimited configuration files by comparing and/or executing the commands in step 6 of the following article:

Reset MailEnable Permissions

If you have changed your default installation to use the MailEnable database provider and are using an SQL database server while getting this error then ensure that the database is online. If the database is online then ensure MailEnable services are able to connect and retrieve data from the database tables.

451 Temporary server error. Please try again later.

Error Description: This response is sent by the SMTP server to a remote SMTP Server or SMTP client to indicate that the MailEnable SMTP Server is currently unable to complete the transaction or command. There can often be more information contained within the SMTP debug logs for this error.

Error Resolution: When this error is returned in the logs or to a client then it usually means that the data store in particular the configuration directory data cannot be accessed. The first thing to check is that your hard drive is not full or faulty or in some cases ensure that any quotas enabled on the drive are not being exceeded. Information on these types of problems can usually be found in the server Event Logs.
When using a default install of MailEnable you can check and repair the permissions on the MailEnable TAB delimited configuration files by comparing and/or executing the commands in step 6 of the following article:

Reset MailEnable Permissions

If you have changed your default installation to use the MailEnable database provider and are using an SQL database server while getting this error then ensure that the database is online. If the database is online then ensure MailEnable services are able to connect and retrieve data from the database tables.

451 Requested action aborted: This mail account has sent too many messages in a short amount of time. Please try later.

Error Description: Means that the SMTP configuration setting to limit the quantity of messages sent per hour has been reached. The message sent in this instance has failed and will need to be retried by the client.

Error Resolution: This feature is disabled by default. You can review this and increase the configured amount of messages per hour or accept the error as correctly limiting a sender or domain.

In the MailEnable Professional or Enterprise manual the settings can be found at:

Post Office Restriction - Administration->Post Office configuration->Restrictions->Limit Maximum SMTP recipients

Mailbox Restriction - Administration->Post Office actions->Create Mailbox->Restrictions->Limit SMTP usage to a maximum of

451 This server employs greylisting as a means of reducing spam. Please resend e-mail shortly

Error Description: This is the temporary error returned to a connecting server when they try to send to an address for the first time while the MailEnable Greylisting spam protection feature is enabled.

Error Resolution: You can in this situation disable the Greylisting service or whitelist the connecting IP. By whitelisting the IP in the Greylisting feature options it means that when this server connects to the MailEnable SMTP service next it will bypass the Greylisting check.

In the administration program the option is configurable at:

Note: MailEnable Professional version users can set this feature at a global level only so the first configuration option below applies. Enterprise users as with most features can also configure this at a post office and mailbox level.

Servers->Localhost->Services and Connectors->SMTP "Properties"->Greylisting (TAB)

In the MailEnable Professional or Enterprise manual the setting can be found at:

Greylisting Global Configuration - Configuration of connectors, services and agents->SMTP Connector->SMTP - Greylisting

Post Office Restriction - Administration->Post Office configuration->Feature Selection->Force Greylisting for all users

Mailbox Restriction - Administration->Post Office actions->Create Mailbox->Spam->Enable Greylisting

451 The IP Address you are sending from was reported as a source of spam. Please contact your e-mail administrator.

Error Description: If a connecting IP has been reported as a spam source via webmail, inbound connections will get this error.

Error Resolution: The IP address has repeatedly been reported as an spam source by webmail users and therefore it is blocked for a configurable period of time. The administrator can unblock the IP address in the administration program under the SMTP->IP Blocking property page.

451 ESMTP MailEnable Service temporarily refused connection at [time] from IP [xxx.xxx.xxx.xxx] because the server is too busy

Error Description: When the SMTP service inbound connection limit is reached the service will reply with this temporary error. Usually in this situation the remote server will automatically retry the send to the service.

Error Resolution: This error is a warning and it should be reveiwed and considered correctly if increasing this inbound thread limit for the error. The default setting for this feature restriction is 32 connections or threads which for most servers will be enough. In high throughput servers you may find that this limit needs to be increased and as such you increase it as you feel, usually 256 is enough for most servers.

If this limit is being reached then you can check the SMTP activity logs and see how many connections you are getting before the error is returned in the logs. While checking make sure the inbound connections appear to be valid and not all coming from one IP or one domain/sender if they are repeating then you should use the other information in the logs to check if the messages are legitimate or the sender needs blocking.

The limit is in place to help prevent spammers or hackers from completing a DOS attack on the server and sending an unlimited and untimed connection based attack to your server.

In some cases if this error continues it can be a good idea to review your DNS Blacklisting service. If you have too many blacklists or one blacklist is timing out on connection then it can tie up your inbound connections for too long. The best way to check this is to disable all blacklists except one along with disabling the URL blacklisting to see if it helps.

MailEnable Knowledge Base article on connection limit

In the MailEnable Professional or Enterprise manual the setting can be found at:

Configuration of connectors, services and agents->SMTP Connector->Inbound->Maximum number of concurrent connections

451 ESMTP MailEnable Service temporarily refused connection at [time] from IP (xxx.xxx.xxx.xxx) because of policy violation

Error Description: This response is sent by the SMTP server when the connecting IP address is registered in the internal IP abuse register. This register contains the IP addresses that have failed too many authentication attempts over a short period of time. IP addresses will be listed if they fail to authenticate over 10 times in less than an hour. When this happens the connection is blocked, but will be removed from the register after one hour.

Error Resolution: If the user being blocked is valid, then likely it indicates they have entered the incorrect username/password into their email client settings. They will need to correct these and wait an hour for the IP address to expire in the register. If immediate access is required you would need to either add the IP address to the SMTP whitelist, or restart the SMTP service. If the abuse option needs to be disabled this can be done through the administration program. Expand the Servers branch, right click on the localhost icon and select Properties from the popup menu. In the window that appears, click the Policies tab and the option is Enable Abuse Detection and Prevention.

452 Too many recipients

Error Description: Means that the SMTP configuration setting to limit the inbound recipients per transaction or message has been exceeded.

Error Resolution: This error is a warning and it should be reviewed and considered correctly if increasing this limit. The limit is in place to help prevent spammers or hackers from completing a DOS attack on the server and sending to a large amount of recipients in one connection. You may need to increase or disable this setting if you are sending mail outs as this error can be triggered when you are trying to send a mail out from a script or send mail program.

MailEnable Knowledge Base article on error

In the MailEnable Professional or Enterprise manual the setting can be found at:

Configuration of connectors, services and agents->SMTP Connector->SMTP - Security->Restrict the number of recipients per email

452 You are not permitted to send to remote domains

Error Description: When this error is shown in the client and/or logs it means that the internal MailEnable configuration setting to limit a mailbox, post office or server has been enabled. By default this setting is not enabled but when changed it can prevent a singular mailbox, or all mailboxes in a domain or even on the server to only be able to send locally to their own domain.

Error Resolution: If this error is believed to be in error then it can be disabled in the ME Admin MMC. In each of the configuration options below you can change the option to allow the mailboxes to send to local and remote domains or restrict mailboxes to only send to local addresses.

Note: MailEnable Professional version users can set this feature at a global level only so the first configuration option below applies.

The first place to check for this setting is at the global level in the ME Admin MMC at:

ME Admin MMC->Servers->Localhost "Properties"->Policies (TAB)->Sender Policy

If the setting above is set to the option "Sending policy determined by postoffice" then you need to check the following place:

ME Admin MMC->Post Offices->[Post Office Name] Properties->Restrictions (TAB)->"The sender policy determines whether users can only send messages to a local domain"

If the above setting is set to "Sending policy determined by mailbox" then you need to check the following place.

ME Admin MMC->Messaging Manager->Post Offices->[Post Office Name]->Mailboxes->[Mailbox Name] "Properties"->Restrictions (TAB)->"User can only send to their local domain"

In the MailEnable Professional or Enterprise manual the settings can be found at:

Global Restriction - Administration->Server Configuration->Policies->Sender Policy

Post Office Restriction - Administration->Post Office configuration->Restrictions->Same Domain Restriction

Mailbox Restriction - Administration->Post Office actions->Create Mailbox->Restrictions->Local Sender Restriction

500 Message rejected because it contains links to an IP address that is blacklisted

Error Description: As a message is being received the SMTP service will resolve links in the message and check these against the configured blacklist. If the destination IP from the resolve is listed in a configured blacklist the message will be rejected with this error.

Note: We are assuming that the default setting in the blacklisting action feature is set to "Don't Accept Email". If this setting is configured to "Mark As Spam" then the message will be accepted and processed by internal filter actions.

Note: When URL blacklisting is executed we check the first section of the message only, about 20 lines. Checking large messages with many links can affect performance. In most situations, if not all, this is enough as spammers do not tend to send many links or large messages.

Error Resolution: The best resolution if you want to receive messages from the sending server is to alert the connecting server administrator that they are sending message links that are listed on a blacklist. In some cases it can be easier to whitelist their IP in the SMTP whitelist option as this will bypass any URL Blacklist checks on the inbound. You can find out more on this rejection in the SMTP debug logs it should also list the blacklist name that the connecting IP was found in.

In the MailEnable Professional or Enterprise manual the settings can be found at:

Global Restriction - Configuration of connectors, services and agents->SMTP Connector->SMTP Reverse DNS blacklisting

500 Syntax Error, command unrecognized

Error Description: This error means that a remote client or server has sent a command that is not recognized by the MailEnable SMTP service.
Error Resolution: The best way to find out more about this error is to check the SMTP activity log at the time of the connection as the command will be listed in the log transaction.

501 Syntax error in parameters or arguments

Error Description: This error means that the remote server is sending incorrect commands through to the server. Often this can occur when the message contains a line that is too long and as such cannot be read by the MailEnable SMTP service.

Error Resolution: Check the SMTP activity and debug logs in this situation as there should be more information on what is occurring. If the logs do not help then check how the message is being sent to see if you can find anything that is abnormal.

501 Invalid Address

Error Description: This error means that the address format used in the sending client is not correct. Usually this is checked in a standard retail client but when using scripts or web pages it may not be the case.
Error Resolution: Check the SMTP activity logs as they should show what format and what characters are being used for the addresses. Check in particular for incorrect characters, here is a list of correct email address characters;

Use any ASCII alphanumeric character plus (`!', `#', `$', `% `&', `*' `+', `-' `~', and whatever you can find in between ASCII 33 and 47).

In short, you should use lower case characters, numbers and the underscore to create your email address.

501 Your domain does not seem to be valid, Could not find MX record for your domain.

Error Description: This error means that the sending email address contains a domain that is not a registered domain name.

Error Resolution: This check is done when the following feature is enabled. The sender should check their email client settings and ensure that their configured email sender address contains a correct and valid domain name after the @ symbol.

In the MailEnable Professional or Enterprise manual the setting can be found at:

MailEnable Manual - Configuration of connectors, services and agents->SMTP Connector->SMTP -Security->reject mail if sender address is from an invalid domain

502 Command not implemented

Error Description: This error means the remote client or server is trying to send a command that is not supported by the SMTP service.

Error Resolution: Use the SMTP activity logs to find out what command was sent to the MailEnable SMTP service.  The commands that MailEnable lists and can use are listed in the SMTP service on the Advanced SMTP tab if the command is not listed then it is not supported or incorrect.  On this tab the commands can also be enabled or disabled the feature can be found in the following location of the ME Admin MMC:

ME Admin MMC->Servers->Localhost->Connectors->SMTP "Properties"->Advanced SMTP (TAB)->Allowed SMTP commands

503 Bad sequence of Commands

Error Description: The error means that the remote client has sent a command to the server that is not in the correct and recognised order for the SMTP service.

Error Resolution: Use the SMTP activity logs to find out what the commands were and that they were issued in the correct order.

503 Bad sequence of commands.  You must specify the recipients of a message before you can send it

Error Description: The error means that a client or server has tried to send a message to the MailEnable SMTP service without the presence of or a correct SMTP address in the TO, CC or BCC field.

Error Resolution: Check the client that is sending and determine why it is not correct you may also find out more in the MailEnable SMTP activity log.

503 Bad sequence of commands.  Could not process DATA command when in this state

Error Description: The error means that a client or server has tried to send a message to the MailEnable SMTP service but has sent the DATA command out of sequence.

Error Resolution: Check the client that is sending and determine why it is not correct usually you will see that the client is sending a DATA command while the SMTP service is expecting another command like RCPT TO, EHLO

503 Bad sequence of commands.  Could not process RCPT command when in this state

Error Description: The error means that a client or server has tried to send a message to the MailEnable SMTP service but has sent the RCPT TO command out of sequence.

Error Resolution: Check the client that is sending and determine why it is not correct.  Usually you will see that the client is sending a RCPT TO command while the SMTP service is expecting another command.

503 This mail server requires authentication when attempting to send to a non-local e-mail address.  Please check your mail client settings or contact your administrator to verify that the domain or address is defined for this server.

Error Description: This error means that the server or client has connected to the MailEnable SMTP service but has not entered a RCPT TO mail address that exists on the server but the domain for the that address does exist on the server.  The order of checks in this situation are; 1. Does the domain exist on the server (Yes) 2. Does the address exist in the address-map.tab file or table on the server (No) 3. Has the client authenticated. (Due to earlier No at 2 this check has not occurred. As the connection has not authenticated meaning that one of the options above in 1 or 2 have not been met then the error is returned.

Error Resolution: If the address is thought to exist on the server then you need to check the SMTP activity logs for the transaction and then the debug log to see if there are any error descriptions that better explain what happened when the address was sent to.  Then you should check your configuration to ensure that the address does exist.  It can also be a good idea to check the address-map.tab file in the MailEnable\Config directory or relevant database table for a line that contains the mailbox name in question.  If you are checking why the sender could not relay through the server then you should at this time check the client settings and ensure that the outbound settings in the client are configured as such so they can relay through the server to non local email addresses. 

503 Too many invalid commands were received.  Terminating Session

Error Description: This error means that the threshold of the MailEnable SMTP security feature has been reached for too many invalid or unrecognized commands sent to the server.

Error Resolution: If this error is not working the way you expected then you can disable the feature or increase the configured limit so the connection is not dropped prematurely.   In the ME Admin MMC the option is configurable at: ME Admin MMC->Servers->Localhost->SMTP "Properties"->Security (TAB)->Connection Dropping In the MailEnable Professional or Enterprise manual the settings can be found at: Configuration of connectors, services and agents->SMTP Connector->SMTP Security->Drop a connection when the failed number of commands or recipients reaches.

504 Access to this user account has been denied by the mail administrator

Error Description: When this error is returned to a client it means that the mailbox has been configured by an administrator to not allow authentication.  Enterprise users may have a mailbox placed into this reject authentication status if the mailbox reaches the Server Password Policy lockout limit.  The Server Password Policy lockout limit in the ME Admin MMC is configurable at: ME Admin MMC->Localhost "Properties"->Policies (TAB)->Password Policies In the MailEnable Professional or Enterprise manual the settings can be found at: Administration->Server configuration->Policies

Error Resolution: You can remove the mailbox authentication lock from the mailbox in the mailbox properties within the ME Admin MMC. In the ME Admin MMC the option is configurable at: ME Admin MMC->Messaging Manager->Post Offices->[Post Office Name]->Mailboxes->[Mailbox Name] "Properties"->General (TAB)->Prevent user from authenticating. In the MailEnable Professional or Enterprise manual the settings can be found at: Administration->Post office actions->Create mailbox->General->Prevent user from authenticating

504 User account has been disabled by the mail administrator

Error Description: When this error is returned to a client it means that the mailbox has been configured by an administrator to not allow authentication. 

Enterprise users may have a mailbox placed into this reject authentication status if the mailbox reaches the Server Password Policy lockout limit. 

The Server Password Policy lockout limit in the ME Admin MMC is configurable at:

ME Admin MMC->Localhost "Properties"->Policies (TAB)->Password Policies

In the MailEnable Professional or Enterprise manual the settings can be found at:

Administration->Server configuration->Policies

Error Resolution: You can remove the mailbox authentication lock from the mailbox in the mailbox properties within the ME Admin MMC.

In the ME Admin MMC the option is configurable at:

ME Admin MMC->Messaging Manager->Post Offices->[Post Office Name]->Mailboxes->[Mailbox Name] "Properties"->General (TAB)->Prevent user from authenticating.

In the MailEnable Professional or Enterprise manual the settings can be found at:

Administration->Post office actions->Create mailbox->General->Prevent user from authenticating

550 Requested action not taken: mailbox unavailable or not local

Error Description: This error means that the server or client has connected to the MailEnable SMTP service but has not entered a RCPT TO mail address or domain that exists on the server.  The address is checked in the local configuration files in particular the address-map.tab file or database table.

Error Resolution: The resolution here really resolves around when you think this error is being returned when it should not be.  If the address is thought to exist on the server then you need to check the SMTP activity logs for the transaction and then the debug to see if there are any error descriptions that better explain what happened when the address was sent to.  Then you should check your configuration to ensure that the address does exist.  It can also be a good idea to check the address-map.tab file in the MailEnable\Config directory or relevant database table for a line that contains the mailbox name in question. 

550 Requested action not taken. The domain you are sending from is not permitted to access this

Error Description: When this error is returned to a client it means that the domain has been blocked from sending to any address in the receiving post office.   

In the administration program this is configurable at:

MailEnable Management->Messagi->Post Offices->[Post Office Name]->Domains->[Domain Name] "Properties"->Blacklist (TAB)->Domains

In the MailEnable Professional or Enterprise manual the settings can be found at:

Administration->Post office actions->Create domain->Blacklist

550 A user policy is preventing you from sending e-mail to this address. Please contact your e-mail administrator.

Error Description: When this error is returned to a client it means that the domain has been blocked from sending to the recipient by the recipient themselves. This is done by the recipient in their webmail options, under the Mail->Blacklist option.

Error Resolution: The recipient needs to log into their webmail account, and under their Blacklist options remove the sending domain or email address.

550 This mail server requires authentication (1) when attempting to send via this SMTP (submission) port

Error Description:  When this error is received it means that the MailEnable server SMTP service has been configured to force all inbound connections to authenticate. This setting is normally not enabled for the default port 25 unless you are behind a antispam/antivirus proxy or service, as otherwise it will prevent you from receiving email from remote servers.  

In the administration program this is configured by expanding the MailEnable Management->Servers->localhost->Services and Connectors branch, right clicking the SMTP icon and selecting Properties from the popup window. Click the Inbound tab and then the Settings button under the Port Settings heading. The option is Requires connections to authenticate before sending email.

In the MailEnable Professional or Enterprise manual the settings can be found at:

Configuration of connectors, services and agents->SMTP Connector->Inbound->Requires connections to authenticate before sending email

Error Resolution:  The resolution is determined by whether you want this feature to be enabled or not.  If you are getting this error when you are not expecting then ensure that this feature is not enabled for either SMTP port.  If you require this feature and understand what it does then ensure any servers that are required to send through the server and not authenticate are added to the inbound IP relay list.

551 This mail server requires authentication before sending mail from a locally hosted domain. Please reconfigure your mail client to authenticate before sending mail.

Error Description: This error means that a server or client has connected to the SMTP service to send email, using a sender address domain which exists on the mail server, but has not authenticated. For this to occur the Address Spoofing option has to be changed to prevent this. For example, if a client is sending with the from address of bob@example.com and the example.com domain exists and the connection has not authenticated, then this error will occur. This option is configured under the SMTP security options "Address Spoofing" located under the "Security" tab of the SMTP properties. More information here: https://www.mailenable.com/documentation/10.0/Enterprise/SMTP_props_-Security.html

The 551 error can also mean that the mailbox that has been entered into the MAIL FROM address line is local on the server but has been disabled on the server by a server administrator or in some cases a control panel. 

This can be resolved by one of the following:

Configure the client to authenticate. If the sender is an email client, it needs to be configured to authenticate with a username/password against the mail server.

Disable Address Spoofing:

• Within the administration console expand the Servers->localhost->Services and Connectors branch
• Right click on SMTP and select "Properties" from the popup menu
• In the SMTP properties window navigate to the "Security" tab
• Click on the "Address Spoofing" button and select the option: Anyone can spoof sender addresses
• Click OK and then Apply

Allowing Authorised connections (privileged IP relay list) to spoof sender addresses:

• Navigate within the administration console to: servers > localhost > Connectors > SMTP
• Right click on SMTP and select "Properties" from the popup menu
• Navigate to the "Relay" tab and select the option "Allow relay for privileged IP ranges"
• Click on the button "Privileged IPs..."
• Tick the option for "Denied relay rights" and clkick the "Add" button to add the IP address of the server/client machine
• Click Close and then Apply.
• Next navigate to the "Security" tab and click on the "Address Spoofing" button.
• Select the option for "Authorized connections can spoof sender addersses".

If the mailbox has been disabled then you can find the setting for this in the following location. 

In the ME Admin MMC this is configurable at:

ME Admin MMC->Messaging Manager->Post Offices->[Post Office Name]->Mailboxes->[Mailbox Name] "Properties"->General (TAB)->Domains->Mailbox is disabled

In the MailEnable Professional or Enterprise manual the settings can be found at:

Administration->Post office actions->Create mailbox->General->Logon disabled

551 Sender address is not valid for your login.  Check your email program settings

Error Description: This error is returned when a client is connecting to relay through the MailEnable server and has authenticated with a correct mailbox address but in the sender field of the mailbox the address does not match.  If this was not prevented it means that a mailbox on the server can authenticate correctly as one address but be able to send with a different from address in effect the sender would be creating a forged email.

Error Resolution: If you want to allow these email addresses to be different then you will need to disable the security feature in the SMTP options.

In the ME Admin MMC this is configurable at:

ME Admin MMC->Servers->Localhost->Connectors->SMTP "Properties"->Security (TAB)->Authenticated senders must use valid sender address

In the MailEnable Professional or Enterprise manual the settings can be found at:

Configuration of connectors, services and agents->SMTP Connector->SMTP Security->Authenticated senders must use valid sender address

552 Message size exceeds fixed maximum message size

The outbound SMTP limit which places a limit on relayed messages is configured at the following location:

ME Admin MMC->Servers->Localhost->Services and Connectors->SMTP "Properties"->Outbound (TAB)->Limit outbound message size

554 The IP address of the sender (xxx.xxx.xxx.xxx) was found in a DNS blacklist database and was therefore refused

Error Description: This error means that an inbound connection has been detected as being listed in one of your configured DNS blacklists within the SMTP options.

To find out more about this feature check the MailEnable manual:

In the MailEnable Professional or Enterprise manual the settings can be found at:

Configuration of connectors, services and agents->SMTP Connector->Reverse DNS blacklisting

Error Resolution: The resolution in this situation varies depending on the inbound connection itself and your verification of the validity of the sender.  In short if the sender is blacklisted and you want to receive mail from this sender then you should suggest/request that they remove themselves from the blacklist (Click here for more)  remove themselves from the blacklist.  In some situations this resolution can be too slow or troublesome and as such you can either stop checking this particular blacklist by removing it from the SMTP blacklist options configuration or you can add the connecting IP to the Whitelist of the SMTP service this will ensure that any future connections from this IP bypass the blacklist check.

554 The IP address of the sender (xxx.xxx.xxx.xxx) does not match the SPF record for the sender domain

Error Description: This error correlates to the SPF checking feature within the MailEnable SMTP service settings.  The SPF feature checks for a valid SPF record to be configured in DNS and then acts on this according to your actions configured in the SPF feature within ME Admin MMC.

To find out more about this feature check the MailEnable manual:

In the MailEnable Professional or Enterprise manual the settings can be found at:

Configuration of connectors, services and agents->SMTP Connector->Sender Policy Framework (SPF)

Error Resolution: In a similar manner to the Blacklisting feature the resolution in this situation varies depending on the inbound connection itself and your verification of the validity of the sender.  If the sender is rejected in this situation and you want to receive mail from this sender then you should suggest/request that they correct their SPF record and /or ensure that they have one configured (Click here for more) correct their SPF record and/or ensure that they have one configured.  In some situations this resolution can be too slow or troublesome and as such you can either turn off the checking of SPF altogether or you can add the connecting IP to the Whitelist of the SMTP service this will ensure that any future connections from this IP bypass the SPF check.