How to diagnose outgoing mail problems and delivery delay notifications


How to diagnose outgoing mail problems and delivery delay notifications. 

If it is possible to send mail locally (from one account to another on the server) but are not able to send mail outside of the domain of server, this article will assist with diagnosis of the issue. 


Checking Firewalls

It is often configuration of a firewall or proxy server that does not allow the mail traffic to send or receive remotely. To help diagnose this, use the Telnet command. Further information on using the Telnet command can be found at: Article ME020207

SMTP Check

>C:\telnet 25

A successful attempt will show a connection and subsequent welcome message as outlined below;

220 ESMTP MailEnable Service, Version: --10.30 ready at 07/03/20 19:54:57

If the firewall or proxy is not allowing SMTP traffic out then the following will be displayed;

Connecting To not open a connection to host on port 25: Connect failed

DNS Configuration

If messages are being dispatched by the server and mail is still not being delivered, then the next thing to check is whether the mail is being addressed and delivered correctly. Checking the SMTP debug and activity logs may show reasons for mail delivery failure.  Two links that can help diagnose any DNS issues are as follows;

The MailEnable utility will show some basic information on a domain and the relay settings. The MXToolbox site will give a more comprehensive report of the status of the DNS settings.

Refused Connection

If a mail server is refusing connection when trying to send mail, the logs will report that the connection was refused. If there are many lines in the logs stating that the connection was refused, then it is likely that a PTR record has not been set up for the server, or the server IP address has been blacklisted on a Reverse DNS Blacklist. A basic check for blacklisting, and/or to check for a PTR record can be done here:

Delivery Delay Notifications

If a user is receiving delivery delay notifications, the message is most likely still queued for outgoing delivery on the MailEnable server. Determine why messages are generating delay notifications by reviewing the SMTP Activity and Debug logs. Use the MailEnable log analysis utility (available from to analyse the log files. You can view the SMTP outbound message queue with a summary description outlining why the delay occurred. Log files can be opened from within the MailEnable Administration program.

Search the Activity log for the mail address of the sender who is receiving the Delivery Delay notification. This will identify where the message is actually attempting to be sent. Also, inspect the MailEnable SMTP Outgoing Queue and determine the Message ID, and search the log for this.

Once the SMTP transactions have been located in the Activity Log, review the Debug Log for entries that same time period. The combination of these two logs should provide enough information as to why the message is not being sent.

Client and Relay settings preventing mail send

There are various reasons why this can occur:

  • SMTP Relay settings
  • Incorrect credentials
  • 'My account requires authentication' not enabled in Microsoft Outlook (or a similar feature in other email clients)

On a new install, MailEnable sets the following relay settings:

- Allow relay for authenticated senders

- Allow relay for privileged IP ranges

The first option, 'Allow relay for authenticated senders' means that only email clients that send a username and password from an active MailEnable mailbox will be able to send email to a non-local email address. So in order to send email to non-local addresses, SMTP authentication needs to be enabled on the email client.

  • If SMTP authentication is not enabled, the message "503 This mail server requires authentication. Please check your mail client settings." will appear when trying to send email. In Microsoft Outlook SMTP authentication can be enabled by setting the 'My outgoing server (SMTP) requires authentication' checkbox in the account settings. The 'Allow relay for privileged IP ranges' in the MailEnable administration program allows the IP address to relay email without sending a username and password, in order to allow programs and websites on the local server to send out email.
  • Ensure that the username to login to web mail is formatted in the following way: mailboxname@postofficename and not mailboxname@domainname. If you need to allow users to log into services with an email address that is mapped to a mailbox, then you need to enable the option to do this in the administration program.


How to diagnose Inbound Message delivery delays: Article ME020318

Error "Message Delivery has been delayed": Article ME020125

Sending or receiving fails on the DATA command: Article ME020063

BUG: "Communications Error: Could not populate sockets address pack" appears in log: Article ME020017

Could not resolve MX list for domain: Article ME020337

Why are messages to external domains not being sent? Article ME020133

PRB: MailEnable will not send mail to remote mail servers: Article ME020014

Product:MailEnable (All Versions)
Class:HOWTO: Product Instructions
Created:20/06/2003 6:51:00 PM
Revised:Tuesday, March 10, 2020