Blacklisting mechanisms in MailEnable


Mechanisms within MailEnable for blacklisting remote mail servers.


SMTP Domain Blacklisting

SMTP Domain Blacklisting allows the creation of a list of domains that are not permitted to send mail to another domain. For example, to prevent a locally hosted domain from receiving mail from This test occurs when the remote SMTP server attempts to issue the RCPT command. When the command is issued, MailEnable checks to determine if the target domain specified in the RCPT command has a rule that prevents it from being able to receive from the domain specified in the sender's address (during the MAIL FROM command). This setting is configured on a per domain basis under the Domain branch of the post office that hosts the domain.

Reverse DNS Blacklisting

Reverse DNS blacklisting defines one or more RBL or ORDB providers that sender IPs are compared with. If the sender's IP address is found in the Open Relay or Blacklist databases then the sender is denied the ability to send mail. This test is performed during the SMTP transaction when the user issues the RCPT command. To take the hard line with those appearing in these lists, there is an optional registry setting that will deny the remote host when they attempt to connect to the MailEnable server. This setting in enabled via the MailEnable Administration Program (Reverse DNS Blacklisting) under the properties of the SMTP Connector.

The registry setting required to enhance its functionality are outlined as follows:

HKEY_LOCAL_MACHINE\SOFTWARE\Mail Enable\Mail Enable\Connectors\SMTP\Reverse DNS Blacklist|Enabled
Value: 0 - Disabled
Value: 1 - Enabled - Deny on RCPT
Value: 2 - Enabled - Deny on Connect

IP Address/Address Range Blacklisting

IP Address range blacklisting can define who can actually connect to the mail server. MailEnable uses the client IP address and compares it to the blacklist defined under the Access Control button on the SMTP Connector's properties. Addresses can be entered with wildcards in them.

For example: 192.168.0.* or individual addresses.


Bayesian Filtering in MailEnable:

Third party spam protection products:

How to reduce incoming spam:

Spam - Frequently Asked Questions:

Product:MailEnable (All Versions)
Class:HOWTO: Product Instructions
Created:4/03/2003 1:49:00 AM
Revised:Wednesday, May 4, 2016