Configuring an Alternate Port for Outgoing Mail Traffic

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Many large ISPs restrict the access to port 25 on their networks to attempt to stem the tide of spam sent out from compromised computers.  If your ISP is restricting access to port 25 you will not be able to send e-mail through your server, but by enabling SMTP (Simple Mail Transfer Protocol) on a different port, like 26, it may be possible to circumvent the restriction.

One quick way to check if your ISP is restricting port 25 traffic is to attempt to telnet to the mail server.  Instructions on how to do this can be found in this article:

Using telnet to check SMTP

If a telnet test shows that your server is inaccessible via port 25 the next step would be to configure the server to listen on an alternative port. The most common alternate port for SMTP traffic is port 26.  Following the instructions detailed below your server and mail client can be configured to utilize an alternative port for SMTP traffic.

Configuring the Server

First the server will need to be configured to listen for SMTP traffic on an alternative port.  Luckily cPanel makes this process very simple using the WHM (Web Host Manager) interface.


  • Login into your server’s WHM (https://[main server IP address]:2087)
  • In the find field search for Service Manager and click on it.
  • On the exim on another port line configure the port for exim to run on (for this guide, 26).
  • Now but a check in the enable box next to exim on another port and click Save at the bottom of the page.


For Plesk on Linux servers please follow the instructions outlined here to configure qmail to listen on an alternative port: Setting alternate smtp port in Plesk on Linux

If connections via port 26 are being denied make sure to check the APF Firewall to assure that port 26 is open.

Configuring the Mail Client

Next, your local mail client will need to be reconfigured to utilize the new alternate SMTP port.  Below are instructions on how to make the appropriate configuration changes for several popular mail clients.


  • Click on Edit and within here click on Account Settings.
  • In Account Settings click on Outgoing Server(SMTP).
  • Highlight the SMTP server being used and click on edit.
  • Now just update the port from 25 to the new value of 26 and then just click Ok to save the change.


  • Click on Tools and within here click on Accounts.
  • Now click on the Mail tab and then double click the account that needs to be changed.
  • Within the account properties click on the Advanced tab.
  • Now just update the port from 25 to the new value of 26 and click ok to save the change.

Mac Mail a.k.a

  • Open Mail and click on the Mail menu bar entry at the top left of the screen, just to the right of the Apple logo. On the menu that appears click on Preferences.
  • In the Preferences screen, click on the Accounts button at the top.
  • Click on your e-mail account name in the Accounts list.
  • To the right of the Accounts list, click on the menu next to Outgoing Mail Server (SMTP) and choose Edit SMTP Server List…
  • If you have more than once SMTP server in this list click on the server name that you are changing.
  • Click on the Advanced tab below the list of SMTP servers.
  • Change the radial button selection to Use custom port: and enter 26 in the text box.
  • Click OK at the bottom of the SMTP server screen.
  • Close the Preferences screen to save your changes.

Related article: How to set up a Mail Account in OS X

If you have tried the steps recommended above and you are still not able to send e-mail using your server with Liquid Web you may need to contact your ISP’s technical support department and find out if alternate port SMTP traffic is allowed at all, or if you will have to use your ISP’s SMTP server.


Liquid Web’s Heroic Support is always available to assist customers with this or any other issue. If you need our assistance please contact us:
Toll Free 1.800.580.4985
International 517.322.0434

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About the Author: J. Mays

As a previous contributor, JMays shares his insight with our Knowledge Base center. In our Knowledge Base, you'll be able to find how-to articles on Ubuntu, CentOS, Fedora and much more!

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