Friday, September 3, 2010

Unable to telnet to remote mail servers on port 25 SMTP

Issue: unable to telnet to port 25 (SMTP) of remote mail servers from windows based machines.

Solution: Your antivirus program may be blocking SMTP connections.

In my case, Avast 5.x blocks all outbound SMTP, IMAP, POP and NNTP connections by default. It's supposed to prompt you when it detects an unsecured connection, but I suppose that's only from actual mail clients, not from the CLI.

Avast specific solution:
1) Open Avast Control Panel
2) Click on Mail Shield
3) Click Expert Settings
4) Click on SSL accounts
5) Add the host name/ip, protocol, port and type of security your connection will use
6) OK your way out of there

If all else fails, turn off Avast/AV completely and test your connection.

This worked for me on Windows XP, Vista and Windows 7.