SBC Port 25 SMTP filtering

[Chris]

It looks like SBC has began to block SMTP port 25 traffic to their subscribers.

See this help article:
http://help.sbcglobal.net/article.php?item=4640

[fallguy]

The solution is to use port 587, which is the standard port for mail submission.

[batmans_byte]

Hi --

Tried port 587 as outgoing email, w/ mail.thn.org (my account on HardHat), that didn't go through. SBC recommends using their outgoing email servers ... smtp.swbell.yahoo.com.

Tried that, worked once, anyways. But wondering if we're going to get blocked by other servers spam filters because coming from different domain that our reply to address?

sbc also says that they will unblock port 25 upon request, and that's probably what we'll do.
using smtp.swbell.yahoo.com works for now.

Kirk B.

[Chris]

Kirk,

Not sure what fallguy is referring to with port 587.

I would stick with SBC's SMTP servers for now. You shouldn't have any problems because your SMTP doesn't jive with your reply-to. The only other option is to ask SBC to remove the filter from your account.

[Chris]

Another alternative is to tunnel port 25 over SSH. This does work and is fairly easy to do.

Basically, you login using SSH and then setup a tunnel for port 25/localhost.

Here is a pretty decent tutorial on how to do it with PrivateShell. This tutorial should provide a good foundation for any SSH client that supports tunneling.

http://www.privateshell.com/docs/howto_email.htm

Hope this helps...

[fallguy]

I was referring to RFC 2476 Message Submission.

The idea is that port 25 is for server-to-server transmission of messages. Port 587 is for message submission -- that is, client-to-server. Read the RFC and you'll learn that there are differences. In short, message submission agents are responsible for a certain amount of policing, such as making sure all the addresses have correct syntax, that each message has a message ID and date, and so forth. Policing doesn't just mean that the MSA blocks messages, rather that it completes them if necessary. An MSA might add a message ID, for example. If MSAs take on this responsibility, then MTAs don't have to. So it makes a lot of sense.

MSAs also solve the problem of port 25 blocking. :-) The MTA at port 25 is for incoming mail from other servers. The MSA at port 587 is for outgoing mail. The rationale for blocking port 25 is to fight spam. There is no such rationale for blocking port 587. That's why it's the solution for clients that have SBC for their ISP.

When you configure Outlook and enter the hostname of the SMTP server, you are actually entering the hostname the MSA. Unfortunately, MSAs on port 587 are not common yet. The mail server still acts as an MSA, only on port 25.

Now, we just have to learn how to configure sendmail to operate as an MSA.


Kirk,

Not sure what fallguy is referring to with port 587.

I would stick with SBC's SMTP servers for now. You shouldn't have any problems because your SMTP doesn't jive with your reply-to. The only other option is to ask SBC to remove the filter from your account.