collect: premature EOM: Error

The following error message came up in the receiving mail server
sendmail[49850]: l948Lq349850: collect: premature EOM: Error 0

l948Lq349850: collect: unexpected close on
connection from server.my.domain, sender=: Error 0


What normally caused such errors (which seem to be a timeout
from the upstream mail relay to the receiving mail server)

Anything to do to improve things?