Outbound mail signing…?

Question

My scenerio is

" php application---->Load Balancer----->smtp server...>relaying

My load balancer receiving mails from php application from different domains now for DKIM we need to sign by DKIM keys for each domain. this is very difficult to implement but now.. I want that when my smtp(multiple) relay mail it sign outbound mails by its own Domain keys for all outbound mails which are from different domain..?

Answer 1

If you're running OpenDKIM, you can use the KeyTable file to specify which key is associated with which domain. Something like:

default._domainkey.example1.com example1.com:default:/etc/opendkim/keys/example1.com/default
default._domainkey.example2.com example2.com:default:/etc/opendkim/keys/example2.com/default

The key default._domainkey.example1.com will be used to sign email for example1.com, and so on.

In the SigningTable, you can also have OpenDKIM match on the From: line of the email, so individual users can be signed using different keys.

OpenDKIM documentation is here.