I'd love it if Airmail could learn to identify spam emails and mark them for possible deletion for me.
Spam identification with all the false positives and negatives is a messy business, and requires a lot of development. As there are spam engines that integrate nicely with Airmail, IMHO, users are better off using one of them over having one developed for Airmail.
A couple of simple improvements would provide 90% of the benefit:
1. if a from Address is in the SPAM folder, place all further emails from that From into SPAM
2. Modify the More/Block function to block at the DOMAIN level not just the specific email address. eg. When in SPAM folder, select email, right click, select MORE, Select Block show email address and the domain for that address as separate selections.
3. Let us see the REAL From address, And Block that!