[plug] sendmail - unexpected close on connection

[ryan at is.as.geeky.as]

Howdy to the plugged,

Recently my sendmail server gives the sporadic error as such to incoming messages:

   ----- The following addresses had permanent fatal errors -----
<address at goes.here>
    (reason: 354 Enter mail, end with "." on a line by itself)

The offending receiving sendmail logs show this:

Feb  6 14:27:11 slowest sm-mta[18429]: h166P36C018429: collect: unexpected close on connection from xxxxxxx, sender=<ryan at is.as.geeky.as>
Feb  6 14:27:11 slowest sm-mta[18429]: h166P36C018429: from=<ryan at is.as.geeky.as>, size=10, class=0, nrcpts=1, proto=SMTP, daemon=MTA, relay=xxxxxxx [x.x.x.x]

The sending sendmail log shows:

Feb  6 14:23:37 localhost sendmail[5409]: h166MxRB005393: mail.slowest.net.: SMTP DATA-1 protocol error: 250 2.1.5 <xxxxxx at xxxxxx>... Recipient ok
Feb  6 14:23:37 localhost sendmail[5409]: h166MxRB005393: to=<xxxxxxx at xxxxxx>, delay=00:00:37, xdelay=00:00:05, mailer=esmtp, pri=300597, relay=mail.slowest.net. [203.15.140.22], dsn=5.5.0, stat=Remote protocol error
Feb  6 14:23:39 localhost sendmail[5409]: h166MxRB005393: h166NRRp005409: DSN: Remote protocol error

I first noticed this type of error many months ago when sending stuff to a friends MDaemon server and assumed it was an MDaemon/Windows specific problem.  Now that my sendmail server has done this I've changed my opinion on the matter.

Is is possible that my DSL is dropping a few packets at a critical time or is there something more tangible I can pin this on?  If it is just as it says - a loss of connection, I would have though such an error would return transient and not permanent as it does.  Anyone care to comment?

Thanks,

Ryan