I don't know if somebody is attacking my email server (slackware, sendmail), or it is just an error?

I get in my maillog several days this error messages:

SYSERR(root): timeout writing message to mx.somedomain.com.: Broken pipe
flags=4406c<CACHED,ESMTP,SIZE,8BITMIME,INMIME,PIPELINED>, errno=32, herrno=1, exitstat=75, state=8, pid=0, maxsize=18000000, phase=client DATA 354, mailer=esmtp, status=4.4.2, rstatus=(null), host=mx.somedomain.com., lastuse=Sat Nov 21 11:23:29 2008\n

It repeats again and again, there are some more lines. I will post them if it will be needed.

Please help, when the sm-mta gets into DATA 354 state the server freezes.

Looks like a power connection to me, the connection times out while sending the mail.