Hi, I just wondered if anyone here had any suggestions for this issue we
We provide a paid SMTP relay service to some of our customers who have
ISPs with awful SMTP relay services.
One constant issue we have is that several of our customers insist of
setting their internal mail servers up to forward all mail for certain
users back out to gmail addresses. That means that they send bucketloads
of spam (incoming spam to them, which then gets forwarded back to our
servers). What then happens is that Google (reasonably understandably)
start limiting our servers from sending mail to them, and they even seem
to start rejecting legitimate mail just because it's come through our
servers which are also sending 'spam' to them.
We do tell the customers not to do this. They do it so they can get
their mail at home, so we tell them it's probably better to simply allow
access to their internal mail server from the Internet (they have IMAP4,
so it's a nice user experience as well), but they still want to forward
the mail back out again regardless.
What I've started doing is detecting this indiscriminate forwarding from
the customers' MTAs and route that mail to one particular MTA which is
only used for sending the forwarded messages on to Google. Hopefully
that will limit the 'bad reputation' to just that one server's IP address.
We could start passing the outbound mail through our own spam filter as
well, but that's something we're reluctant to do because it'll lead to
Any other ideas or thoughts?
Am I right in interpreting Google's behaviour, or are they clever enough
to detect MTA forwarded messages and not assign poor reputation to the
forwarding MTA in that case?
Is there something clever we should be doing to tell Google what's
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