For years, many hosting providers have been blocking port 25 as an effort to combat spam. While this can help avoid spam abuse on their networks, it does cause problems for legitimate users trying to send email from their servers.
By default, all mail servers use port 25 when trying to relay messages to other servers. By blocking this port, your server cannot connect to these other servers and deliver messages to remote locations.
If this block is in place, you will only be able to receive mail and send mail internally.
For more information on these types of blocks, please see: Why can I receive, but not send, emails?
Before you attempt these methods, you should first review if it is possible to remove the block or if your provider offers a Smarthost solution.
We have details on various providers available, though this does not contain a complete list.
Why is port 25 blocked?
If your provider will not remove the block and they don't offer an alternative method to send mail, you may want to consider a third-party Smarthost, as this is the fastest way to get a relay set up. These would receive the message over an alternate, unblocked port (such as 2525) and then relay it to the destination over port 25 for you.
There are many options available. Here is an incomplete list:
These vendors are not endorsed by or affiliated with cPanel, L.L.C. and must be independantly revieed and implemented.
We have both a general guide, as well as some vendor specific Smarthost configuration guides available.
For self-hosting mail, there are a few options.
You can use another cPanel server on an external network as a relay.
Currently, Mail Node is available to be used for standalone hosted mail using the cPanel and Webmail interfaces to manage.
Linking a Mail Node to a cPanel server, however, is currently experimental. This would enable the main cPanel server to manage email accounts on the remote node.
If you decide to host mail on a non-linked server, either using Mail Node, or with another platofrm, such as Microsoft Exchange Server, you’ll need to set up your cPanel server to understnad that email is sent on a remote host.