rewrite only for SPF enabled domains about postsrsd HOT 2 CLOSED

I am not aware of any good way to do that. You can exclude domains if you know they don't use SPF manually. However, given that the rewrite is envelope-only and thus invisible to the end user, I would not bother.

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I think that should be relatively easy to implement:

You get the envelope e-mail address of sender by postfix (because it is the one you want to rewrite). Just extract domain name from it (you do that anyways to check the list of excluded domains). Do a DNS lookup of the TXT record of the domain extracted. If the TXT as returned by libc/DNS server contains the string "spf", the envelope sender's address is SPF enabled. In that case you need to do SRS. Otherwise it is useless.

This is an additional DNS lookup on every request, but if the mailserver has done the "policy-spf" checks already, the TXT record is in the DNS cache already...

This issue has nothing to do with the fact that the daemon rewrites any address, forwarded or not. This issue is just to disable the rewriting if the sender domain does not require it, because forwarding can be done safely without SRS. If the sender's domain has SPF enabled, you need SRS, so it is better to do it (although not forwarded later, but that's the well-known postfix cleanup limitation).

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