How to process a new letter in Exim?

Question

Exim

User A wrote a letter to user B. A note about this must be written to a text document or database. How can this (the fact that user B has a new unread email) be done?
I read about the "autoresponder", but did not understand whether it can be used at all. And if you check via SMTP, then you need to know the passwords of all users and load the mail server with requests.

Answer 1

I think it is possible in the router for delivery to a local user, add a condition with the execution of mysql-lookup, where to execute insert. https://www.exim.org/exim-html-current/doc/html/sp...
Or, for a transport that delivers to a local user, add a shadow_transport with driver=pipe and pass the email/headers to some external script that either add information about a new letter to the database, or immediately notify the user.