How to control which interface or IP Address is used for outbound mail


How to configure which IP address will be used by MailEnable to send outbound mail via SMTP. 


When two or more interfaces are configured into the same subnet, all interfaces can receive traffic but only one of them will be used for outbound traffic. The first adapter/interface added to the computer is always used for outbound traffic. This can be checked by using the ipconfig command from the Windows Command Prompt. The actual routing and adapter preference is controlled by Windows, and modifying this behaviour can be complicated.


To avoid changing the configuration of the underlying network settings, MailEnable provides the ability to configure which IP Address is used to send outbound mail.

This can be configured from within the MailEnable Administration program under the properties of the SMTP Connector.

1. Open the MailEnable Administration program

2. Navigate to MailEnable Management|Servers|localhost|Connectors|SMTP::Properties

3. Select the Outbound tab.

4. Under the Outbound IP Binding section, it is possible to set the outbound binding to the desired IP address of the server.

There are a few additional possibilities that can be used to change the underlying networking environment to achieve the same:

1. (Simplest) Change the order of the interfaces that are added to the computer and ensure the one to use for outbound is added first.

2. (Simple) Configure NAT (or PAT) on the router hence forcing all Outbound Traffic to appear to have come from the same IP Address.

3. Configure static routes pointing at each specific local interface IP to give the desired outbound route. This can be done by using the route command at the command prompt, but it is complicated and specific to the IP networking typology.


When adding a new IP Address to my server, MailEnable will only bind to a single interface:

Product:MailEnable (All Versions)
Class:HOWTO: Product Instructions
Created:23/05/2003 10:49:00 PM
Revised:Wednesday, May 4, 2016