What's happening is that fetchmail is interpreting the 501 response as a
spam block. It's doing exactly what it's supposed to. You need to fix
your config so it doesn't generate bogus MAIL FROM: lines.
I had a similar experience recently. Unfortunately, I am at the mercy
of a volunteer sysadmin who has been known to be lazy, inexperienced
and just plain bone-headed (me). I've been setting up a second Linux
box on my home network and I thought I had setup a shared home
directory. I wanted to check my mail on the new box, typed in
fetchmail and got a lot of 501 messages along with the exciting news
that the messages had been "flushed."
Turned out that in the stock Redhat 7.1 exim.conf, relays from
localhost are disabled:-( My fault, but what a way to learn. Still
haven't gotten around to making sure that exim is working on the new
box. I'm just trying to remember not to run fetchmail on it until I
am sure that it does work (lazy and boneheaded, I'm sure:-)
In my situation, any mail that my SMTP configuration would reject and
my ISPs would accept is the result of some sort of newbie error on my
part. I would deeply appreciate a "cluelessslusermode" option that
would ensure that any mail that made it to the remote mail server
stayed there until the local delivery agent accepted it or a
responsible adult had determined that it should be deleted. My sense
is that the option should default to true because it might never be
set if the cluelessluser had to be relied on to read the man page to
identify himself:-)
In the past, I've been at the mercy of a professional incompetent
sysadmin who was nowhere near as sincere and well-meaning as I am, so
maybe the name should be changed to "deleteonSMTPerror" or somesuch.
Thanks for the very useful product. Really like the quotes you use in
your signatures. I've been collecting them.