In discussions here there is a scenario given where a MAIL-FROM, one
or more RCPT-TOs, and a DATA commands are sent as a single PIPELINE
burst thus going into DATA more before the server has responded to
the MAIL-FROM and RCPT-TO commands. This is IMO a BUG (or at least a
Design Flaw) on the part of the MUA which should NEVER send that DATA
under the assumption that the MAIL-FROM and RCPT-TOs will be
accepted. It should wait it gets the queued replies and parse them
BEFORE it assumes it has permission to send the DATA and go into DATA
mode. This will allow it to work the same as if it were NOT in
PIPELINE mode and react to the replies that the Server is sending it.
A note to this effect would help avoid this type of broken behavior.