[OB] failures of aol/aim mail

[Charlie Smith]

If you don't have anything to do with setting up email software,
and if you are not an AOL subscriber then you can probably skip
most of the rest of this.

If you are running the sendmail mail transport software, or if you
know someone that is using it, AOL made a change about last weekend
that causes their mail to fail when being sent to a site running 
sendmail.  This also means that if you are using AOL and some of
your mail has been bouncing - with a message like 
    [recipient system] not reachable
Then you need to contact the admin of the recipient system and pass 
along this information.

To my personal knowledge, AOL has claimed to several people that
they have not made a change.  Further, AOL has not responded to 
emails I have sent to postmaster at aol.com and other contact emails.
They did make a change about last weekend, 6/14/08.

Here's what's going on.

A standard feature of sendmail is called "greetpause".  This is 
a spam prevention feature that is enabled by default.  In your
system.mc file, this looks like this:

    FEATURE(`greet_pause', `18000')dnl

The greetpause feature was introduced somewhere early in the sendmail 
8.13 timeframe, well over a year ago.  Email is rejected by the 
greetpause feature when it fails to meet the SMTP protocol standards.  

Specifically, when a client (the sender) connects to a mail server
(the receiver) - the client sends a single message to identify itself.
(This is the helo "my-system-name.domain" message).

The client is not supposed to send anything else until after the server
responds with it's identification.  Any client that sends another message
before the server's response is in violation of SMTP the protocol.  Most
spam generation programs will not wait very long before they continue
sending data.  When the client sends more data before the server's response
message, the greetpause feature cuts the connection.

My default greetpause delay period has been 18 seconds, this has been
the case for over a year.

The AOL change is that when they don't get the response in about 10 seconds,
they appear to give up and break the connection.  This is a change made
by AOL in the last few days, since their mail has been waiting for the 
18 second delay until their change.

I have circumvented the AOL problem by making them have only an 8 second
delay.  That appears to work, and AOL email is again being received.

    - Charlie