[Top] [All Lists]

Re: [ietf-smtp] Mail forwarding to Gmail problem/question

2016-02-03 05:08:52

On Feb 3, 2016, at 10:32 AM, Paul Smith <paul(_at_)pscs(_dot_)co(_dot_)uk> 

Hi, I just wondered if anyone here had any suggestions for this issue we 
constantly have...

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.

This is more of a mailop question than an ietf-smtp question.

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 false 

Definitely do some content filtering, but label the mail rather than discarding 

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 happening?

Read this:


ietf-smtp mailing list