smtp2pcng.py doesn't set its exit status, so it often
exits with a non-zero exit status. If it's being used
as a delivery alias in postfix, and it exits non-zero,
postfix reports a delivery error (even though the bug
has been submitted) and the sending system retries the
email again an hour later, and again an hour later, and
... and finally reports
the mail as undeliverable.
The fix is really easy, just add:
on the end of the mainline....