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Comcast blocks port 25

Testing a remote SMTP server is kind of hard when Comcast is secretly blocking all inbound and outbound traffic on port 25. I only figured it out when telnet wouldn't even work. I could've saved myself an hour of frustration if I'd known this. Thanks, Comcrap.

August 15, 2009 @ 8:22 AM PDT
Cateogory: Rants


Quoth Bleys on August 15, 2009 @ 7:59 PM PDT

Try port 587 instead, it's an alternative SMTP port that most ISPs support.

I don't get how telnet is relevant, since it doesn't use port 25 unless you tell it to. Does comcast block port 21 as well?

Quoth Brian on August 16, 2009 @ 5:11 AM PDT

It's my own SMTP server so it wasn't a big deal to set it to listen on another port, but it was annoying. I don't know about 21, I never use FTP, only SFTP.

Telnet is relevant because it's the easiest way to test whether a mail server is up and running. Telnet to port 25 and type all the SMTP commands yourself.

Quoth JohnP on December 10, 2009 @ 12:49 PM PST

I've been running SMTP on Comcast since 1998. Port 25. Residential. DHCP, but my IP doesn't really change much - perhaps once every 3+ years. There's a few websites and other services there too, but I'm not a heavy data user.

If I could get anything like the bandwidth that comcrap provides for a reasonable price elsewhere, I'd switch. I've worked for the big bell guys and don't ever plan on using them for anything again.