We have quite often some complaints from outlook.com and some others "big" mail services, that we are forwarding "spam" to them.
In fact most of the time it's not spam. It's people we're hosting their e-mail (on Smartermail) and are using forwarding their mail to an external mail service.
When these mails are unwanted, they mark them as spam (on their external mail service) and we receive the complaint as the last MTA they see is ours
(Despite we have enabled SRS to avoid the SPF problem with forwarding).
It's most of the time a pain to identify that it was a forward and track down which local mailbox forwarded that "offending" message.
Could it be possible that SmarterMail adds some headers to help identify that the mail was a forward, and which mailbox it was forwarded from ?
I've checked how other mail services handle this, for exemope gmail add these headers to forwarded mails:
X-Forwarded-For: email@example.com firstname.lastname@example.org
So it's easy to identify the mail was forwarded by a gmail account.
Outlook.com on their side add this to forwarded messages:
Another opensource mail solution based on postfix/dovecot/sieve that we are using, add these headers (sieve is doing the forwarding and adding headers for it):
X-Sieve: Pigeonhole Sieve 0.5.2 (7704de5e)
It would be really useful to have Smartermail do something similar when handling automatic forwarding.
Here is another really interresting paper about best practices when handling auto mail forwarding, worth a read:
I particulary like the idea of using a different outgoing gateway only for sending forwards, That way if it's declared at spam, it doesn't lower the reputation of your main outgoing gateway
Unfortunately I guess there is no option in Smartermail to route forwards via another gateway.
It could be done on an outgoing gateway. Reroute the mail if it contains headers indicating that the mail is a forward, but for this, we would need Smartermail to add headers indicating it is a forward :))
Any thoughts / suggestions ?
Thanks a lot