[pfx] Re: Per recipient sender access via an access policy delegation server

John Fawcett via Postfix-users:
> Hi
> 
> I'm posting this message in case anyone would find it useful to have an 
> access policy delegation server that implements per recipient sender access.
> 
> I have been using check_sender_access as a deny list for senders that I 
> want to block from sending me email, usually emails that started off as 
> legitimate but after unsubscribing still keep coming. The issue is that 
> when I block a sender, I do so for any recipients that use the server, 
> not just me. While in practice that hasn't caused many issues, it always 
> worries me that I might block email other users want to receive.

Would a postfwd policy ruleset handle that? 

Unlike access maps that give an answer based on a single property,
policy lookups support multi-criteria decisions by design.

> So I had it in mind to write an access policy delegation server that 
> implements  per recipient sender access. I believe that it's not 
> possible to achieve this within Postfix configuration directly and that 
> the policy delegation protocol was developed just for such use cases. 

Indeed!

> With a little bit of help from AI I have got a working prototype in 
> python that queries a mariadb table. It's a single long running process 
> that can handle multiple incoming connections. The lookup 
> functionality/return codes work similar to access maps, but has the 
> additional key of the envelope recipient address.

Or any other couple dozen attributes.

> I realize that probably other policy servers contain similar 
> functionality bundled with other capabilities, but I decided to do 
> something specific for this single need. At the moment I did this for my 
> own use, but if anyone has a similar need I'd be happy to publish the 
> code, if contacted on or off list.

Thanks for sharing.

	Wietse
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