If you are able to receive mail without issue, but are unable to send mail from your mail client and you are certain your outgoing mail server settings are correct, you might be blocked by your ISP from connecting on port 25.
The default port for SMTP (sending mail) is port 25. Some ISPs block access to port 25 in order to try to avoid some issues with spammers. However, this can also block you from being able to connect to your mail server to send mail through your domain. Alternately, you may have port 25 blocked in your local router or cable modem. This article will explain how to check if port 25 is blocked from where ever you are and what you can do about it.
How to Check if Port 25 is Blocked
Here is how you can check to see if port 25 is blocked. Follow the directions for the OS that you are using locally (not on the mail server itself).
What to Do if Port 25 is Blocked
- Configure your mail client to use port 26 or port 587 for outgoing mail (SMTP) instead. This will usually do the trick.
- On a cPanel server, getting Exim to listen on another port is easy, just check Exim Mailserver on Another Port in the Service Manager feature in WHM and select the port to use (26 is the default), then save changes.
- Contact your ISP to confirm they are blocking port 25. You'll likely need to change the SMTP port (as in step 1 above) to get around this. ISPs rarely open closed ports for non-business internet clients.
- If your ISP says they are not blocking port 25 or 587 and you are still having problems sending mail, check your local router or cable modem to see if port 25 is blocked there.
- If nothing else works, and you have service with HostDime, please contact us and we can investigate.