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AOL blocking outgoing SMTP?

gav on 2004-02-17T00:27:50

Late last week somebody on my box was complaining that they could receive email but not send it. The strange thing is that it was happening from two separate machines that he swears that he didn't touch the settings on. Both use AOL dialup.

After trying to track down the problem and checking the machine in person it seems that AOL is blocking SMTP traffic to my server. I can't telnet to port 25, though I can send mail to another mail server (which has identical settings) on the same subnet. It seems that AOL uses a transparent SMTP proxy which is just not making the connection, checking with tcpdump confirms that no attempt is made to actually connect.

Any ideas? He's already called AOL who claim that they aren't blocking the connection.

AOL dialup email

merlyn on 2004-02-17T00:34:46

AOL dialup email is supposed to go through their hub, if I recall. You shouldn't be able to send directly from an AOL dialup to the world at large. This is to ensure that you're not violating their TOS by spamming.

And I'd say this is a good thing.

smtps

entropic on 2004-02-17T06:40:23

I had a similar problem with aol clients not being able to send ssl/tls mail.

The first hit in google has good info:
http://computing.fnal.gov/email/smtp-server/tls.html

To avoid the aol port 25 proxies, I have aol users send mail over port 26 and I redirect port 26 to port 25 in pf. Seems to work well.

Port 25 blocking

cbrandtbuffalo on 2004-02-17T16:53:28

As a side note, I think this may become more common. They are considering doing it here at the University at Buffalo for internal traffic. The real reason is that people get a virus on their machine that is sending email using port 25, and they don't even know.



But it seems to me this may be staying one step ahead of (behind?) the virus writers because they will already be looking at ways around this.

Re:Port 25 blocking

gav on 2004-02-17T17:17:26

Blocking port 25 would solve a lot of virus (and spam) problems but it does seem very heavy handed to me.

I think we need to be good citizens and provide the same kind of filtering to outgoing mail as we do to incoming. Forcing outgoing mail through a proxy that stopped viruses and restricted the volume for most users (say 50/hour) would contain a lot of problems rather than letting the receiving end deal with it.