Why is port 25 blocked? – cPanel

Question

When trying to send mail from my server, the mail is never sent. Connections to other servers on port 25 refuse to connect. Why is this blocked?

Answer

Many providers block access to send data out on port 25 as a way to prevent spam from being sent from their network, but, as this port is essential for communicating with external mail services, it also prevents mail from being sent for legitimate users.

Note: cPanel offers the option to change the port Exim listens on, but you cannot use alternate ports for sending mail. Other remote servers are not configured to accept mail on non-standard ports.

Some providers block port 25 automatically, but are willing to remove the block if asked. Checking with your hosting provider or Internet service provider's documentation or contacting their support is typically required to remove the restrictions. If your provider is unable to remove these restrictions, you will need to use a relay service.

Here are links to some of these documents from various providers:

If you are a hosting provider with specific documentation you'd like to add to this list, please reach out to your cPanel account manager.

If the provider is not willing to open access, they might provide their own SmartHost or relay. The provider would provide any necessary details for the SmartHost if not configured by default.

If your provider will not unblock port 25 or offer an alternative solution, you can review the following article:

How To Send Email When Your Server Provider Blocks Port 25.

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