I recently decided I'd attempt to set up my own mail server on my CentOS 5 Linode. I followed Linode's guide (https://library.linode.com/email/postfi ... he-mailbox) and despite some hiccups along the way, I'm now able to send and receive mail from my mail client! Unfortunately, there still seems to be issues somewhere in my configuration…

I attempted to help a friend set up his email client to connect to my server. He's able to receive email but not send it. When I take my laptop and go to his house, I'm also unable to send email. I'm using the same laptop and client, so it seems like the IP address is the only thing that changes between his home and mine.

I haven't taken any measures to create white/blacklists for IPs. Does Postfix have any IP-specific rate-limiting or spam defenses that were wrongfully triggered? I read that smtpd_hard_error_limit was IP-specific. Is there a way to see if it is blocking connections? What else could be the cause?

Unfortunately, maillog doesn't seem to give any clues. I see a few instances of this showing up, but I'm not sure if it's meaningful:

Jun  4 08:54:56 ender postfix/anvil[27673]: statistics: max connection rate 1/60s for (smtp:<ip>) at Jun  4 01:51:36
Jun  4 08:54:56 ender postfix/anvil[27673]: statistics: max connection count 1 for (smtp:<ip>) at Jun  4 01:51:36
Jun  4 08:54:56 ender postfix/anvil[27673]: statistics: max cache size 1 at Jun  4 01:51:36

Thanks in advance to anyone who can provide clues or assistance in getting me back on track!

My guess is his ISP is blocking port 25 outgoing. Try using TLS/SSL port 465 (I think it is)

Thanks for the quick reply!

I'll give a different port a shot but I'd be surprised if that's the issues. Both he and I use Comcast and we live pretty close.

Update: Looks like you might be on to something! Comcast says they block port 25 on this page. I opened up both 465 and 587 on my server. I'll ask him to give it another shot tomorrow.

Yep.. Most ISPs will do that, but they should allow 465 (ssmtp) through. Ideally you want to only allow authenticated relaying from users you have/created, over SSL/TLS, so 465 is the port you want.

Alright! Getting closer. He's still unable to get mail, but opening port 465 in the iptables was probably a necessary step forward.

I have a new clue. I noticed after running netstat -ntpl that the server isn't listening to port 465. Could this be another firewall issue? Or have I set up Postfix incorrectly?

- bt


Update: I posted too soon again. I figured out that the ssmtp line in Postfix's master.cf was commented out. Updated and working!