Custom mail server - your own criteria for letters?

Question

Mail server

The essence of the question is simple: I want to raise my own mail server. I already used docker-mailserver for this . But this time you need to implement several "custom" features, namely:

Each time the server receives a letter, in addition to the standard checks, you need to be able to call some of your own. Ideally, it looks like "the server makes an HTTP request at some URL -> sends a letter in the request -> receives a response and acts accordingly."

Ideally, the answer can take the following values:
- Everything is OK
- Not OK, ignore the letter
- Throw a whack at the sender with the text "blah blah blah"
Are there any tools already sharpened for this?

Answer 1

For DDoS immediately. You such antispam want skolhozit?
Such things are done not when a letter is received, but when it is transmitted to the local delivery agent (LMTP). This is specifically done in order to separate the main process of receiving mail - which is rather hard-coded in the RFC - from the handlers.
You will have to cut it yourself, as an example, you can see DSPAM.

Answer 2

Exim implements this at the ACL level at any stage of incoming mail processing.
In your combine, figure out where and how to stick it. But I'm sure it's technically feasible.