Version:            (using Devel)
OS:                Linux

Currently one can only check for "not in addressbook", which is useful for spam-filtering, i.e. as a whitelist.

"not in recently used addresses" would be as useful, since if one sends and email to somebody only once, it is unlikely that one will add that person to the addressbook, yet one surely wants to read the reply.

Assuming that the recipient's address will stay in the recently used addresses for a couple of days and a reply arriving in the same time-span, using the recently used addresses as whitelist would prevent that reply from being marked as spam.