Timout after DATA

[demigh0d]

I've run into a perplexing problem. My mail has been working fine. Recently I noticed emails to craigslist.com (postfix) were bouncing. My logs show that this started on January 1st. Nothing had changed on my server since before the holidays.

After a lot of research, tcp dumps, upgrading sendmail, reconfiguring from scratch, disabling MTU discovery, etc. the problem persists.

The TCP shows the following, in order...

220 mxi1s.craigslist.org ESMTP Postfix
EHLO srv001.mydomain.net
250-mxi1s.craigslist.org
250-PIPELINING
250-SIZE 5242880
250-VRFY
250-ETRN
250 8BITMIME
MAIL From:<user@mydomain.net> SIZE=687
250 Ok
RCPT To:<sale-261825705@craigslist.org>
DATA
250 Ok
354 End data with <CR><LF>.<CR><LF>
{headers & body are sent but no CRLF.CRLF}
{sendmail tries several times to re-send}
421 mxi1s.craigslist.org Error: timeout exceeded
{sendmail ACKs. Then there's a FIN/ACK ACK}
.
QUIT
{CL responds with RST}

For some odd reason Sendmail is not sending the <eod> until AFTER the tcp session is closed.

BTW, craigslist isn't the only domain I'm having this problem with. There are a couple others. But there are hundreds (thousands?) more that I haven't had any problems with so I am completely baffled.

Duane