Spam Frequently Asked Questions


This article covers some of the main features of the inbuilt MailEnable spam and security settings. The document also answers some of the more common questions that MailEnable support often receive in regards to spam protection.


  • What is SMTP Domain Blacklisting?

Blacklisting methods:

  • How do I configure Reverse DNS Blacklisting?

Reverse DNS Blacklisting: 

How can I create and manage my own Reverse DNS Blacklist Server?:

  • How can I block IP addresses using SMTP access control lists?

Blacklisting methods:

  • How can I stop inbound email from senders that are not registered mail servers?

MailEnable provides the ability to check for a PTR DNS record for inbound connections. This can be useful to block email from cable/ADSL connections, which is where a lot of spam originates. This option is defined within the SMTP properties under the 'Security'. The 'PTR Record Check' can be configured to:

  1. Never reject senders
  2. Reject senders without PTR
  3. Refer to System Spam Protection Filter (
  • How can I stop messages that come from invalid domains?

Incoming messages from remote mail servers that are from invalid domains can be prevented by enabling the option 'Sender email domain must be local or resolvable through DNS' within the SMTP propeties under the 'Security' tab. This setting will validate the existence of a mail/return path DNS records for the domain of the message sender address. This also helps validate the authenticity of the sender address.

  • Why do unwanted messages keep getting delivered to a specific mailbox?
  1. The first option to check is if the mailbox receiving the unwanted messages has been set to be a catch-all address for the domain. If a domain has been configured with a catch-all address it will accept all incoming emails even if there is no valid email address mapped to a mailbox in that domain. Therefore access the domain properties and check that the mailbox is not set as the catch-all address (
  2. Check to see if a catch-all address has been configured to redirect to the mailbox receiving the unwanted messages (
  • What is SPF (Sender Policy Framework)? And how can it protect my server from spammers?

SPF (Sender Policy Framework) is a method to help prevent spam and address spoofing. A domain will contain a DNS TXT record that contains a list of servers that are allowed to send emails for that domain. This provides a means of identifying the authenticity of the sending mail server by performing SPF record lookups. If an the SPF record for the domain does not contain the IP address of the sending server it is likely to be considered as a spam.

MailEnable provides options to reject incoming messages that have failed SPF. For more information about SPF please see:

  • Can I use Third-party spam software with MailEnable for spam protection?

Third-party utilities for filtering spam are listed here:

  • What is Bayesian Filtering?

Information regarding Bayesian filtering can be found here:

  • How do I implement spam/message filtering in MailEnable?

Please see:

  • How do I mark messages as spam and have them delivered to a Junk-Email folder?

Please review the following article as it explains how messages are delievred to a mailboxes 'Junk E-Mail' folder:

SMTP Filtering Options

  • Greylisting (Professional and Enterprise versions)

This feature can be found in the SMTP properties->Greylisting window of the MailEnable administration program. Greylisting will change the SMTP service to not accept any message on the first send by the remote server and instead will send back a temporary error (an SMTP error code 4xx). The temporary error will indicate to the sending server to retry. Spammers generally do not retry sending an email, and treat the temporary error as permanent, which effectively stops the spam.

There will be a delay in inbound message delivery where the sender does not authenticate, or has not recently sent to the server. The delay time varies depending on the retry intervals for the sender server, but in most cases will be within 10 minutes. Whitelisted IP addresses bypass greylisting.

  • Outbound Whitelisting

Outbound whitelisting is configured in the SMTP properties->Whitelisting window of the MailEnable administration program. When enabled, the SMTP service will whitelist any IP address it sends email to, assuming that you don't want to block email from IP addresses you send email to.

Global Spam Protection Script

Spam protection within MailEnable is a weighted filtering system that accumulates points for each factor of a message that could be considered spam.  The spam protection values can be found in the spam protection under the Messaging Manager in your MailEnable Administration Program. The goal here is to find a perfect balance of points per message for your spam.   Each one of the values would not necessarily be deem a message as spam on its own but if several fail then the chance of the message being scored being spam is considerably higher.

PLEASE NOTE - The spam protection filter will do nothing to the message except add a header line to the message. This header is then checked when a message is being delivered to a mailbox, and an action may be performed, depending on what the user has configured under their Spam Protection options in webmail. One of the following values depending on the score of points compared to the threshold you set in the spam protection values will be added:

X-ME-Spam: Low

X-ME-Spam: Medium

X-ME-Spam: High

The following articles can help test the spam protection service and provide more information on how to make it more effective:

Webmail -  Report As Spam Option (Enterprise Only)

The MailEnable Webmail client provides an option to report messages as spam. This is done by right clicking on a selected message in the message list and selecting the 'Report as spam' option in the menu. 

Actions can be configured for the 'Report as spam' option within the MailEnable administration console within the 'Webmail' properties node under the 'Spam' tab or via the web administration interface. Please see:


How to reduce incoming spam:

Spam protection feature availability in MailEnable:

Product:MailEnable (Pro-Any Pro-1.X Ent-Any Ent-1.X)
Keywords:spam anti-spam anti spam filters filtering bayesian, SPF, sender policy
Class:FAQ: Frequently Asked Questions
Revised:Tuesday, March 6, 2018