Last week I had a user receive the following two messages:
lost connection with host.domain.com [x.x.x.x] while sending message body
- and -
connect to host.domain.com [x.x.x.x]: server dropped connection without sending the initial SMTP greeting
Both of these bounces came from the same destination. My user had a couple of moderately sized attachments on each message (about 1 MB each).
I would have thought it if was a problem with the attachment size I'd see a different message.