>-> RSET
>451 There is a timeout while waiting for input during server cmd read.

This has to do with sendmail, not LISTSERV.  You probably need to check
the syslog to find out why this is happening.  In any case LISTSERV is
trying to hand mail to sendmail to go out to the recipient and sendmail
is responding with a RSET, which is not good.  If your sendmail was
upgraded along with your OS, my guess is that there's something wrong
with your sendmail setup.

Nathan