[SA-exim] FAQ about forwarded mail?

[Eric Sharkey]

I've searched the sa-exim list archives and I've seen this issue brought
up a few times, but never with what seemed to me to be a definitive
clear answer about how to properly set up a system to handle forwarded
mail.

Forwarded mail is different from non-forwarded mail since rejecting
such messages is likely to produce collateral damage, and grey listing
such messages is actually counter-productive.

Is there a simple guide to configuring sa-exim to never bounce or
greylist forwarded mail?

Eric

[Magnus Holmgren]

Post by Eric Sharkey
I've searched the sa-exim list archives and I've seen this issue brought
up a few times, but never with what seemed to me to be a definitive
clear answer about how to properly set up a system to handle forwarded
mail.
Forwarded mail is different from non-forwarded mail since rejecting
such messages is likely to produce collateral damage, and grey listing
such messages is actually counter-productive.
Is there a simple guide to configuring sa-exim to never bounce or
greylist forwarded mail?

I think the easiest way is to set SAEximRejCond in sa-exim.conf to something
like ${if eq{$acl_m0}{canreject}}. Then you use the power of the ACL system
to determine whether spam can be rejected or must be quarantined.

I have, after require verify = recipient,

accept local_parts = postmaster : abuse
accept hosts = +incoming_relays : ${lookup dnsdb{>:mxh=$domain}}

then some anti-spam measures such as dnslists, then

accept set acl_m0 = canreject

The difficulty lies in identifying forwarded mail coming from many different
places without letting in everything from Hotmail and AOL.