This is impossible.
Amavisd stores very basic info of Sent/Received emails, it doesn't store mail headers, so you cannot view mail headers at all.
Not even the spam score? It would be useful to check how the spam filters are working, even on clean email.
This is what Bayes does, but we don't have proper Bayes implementation in iRedMail.
Check this wiki tutorial for reference:
Maybe the checkboxes/buttons, when selected, could redirect the specified email (or copy of it) to a folder named SPAM (or HAM). Then a cron job would run sa-learn on those folders. Another way could be running queries directly on the bayes database.
The problem is, we are creating a new domain, what should we do with this alias accounts? Forward to an external email address as domain admin? Or forward to another new mail user (e.g. postmaster@)?
I can give you my old server example. It's a multiple domain system. Every alias (abuse, hostmaster, postmaster and webmaster) is created by default when creating a new domain if I choose to (via a checkbox). If I choose to create it, it will be forward to our main domain equivalent address (Ex: postmaster@newdomain.tld -> postmaster@maindomain).