Blacklist of recipient target addresses in the spamfilter (useful for wildcard mailboxes)
I miss the functionality of managing a blacklist of target email addresses in case you have a catchall email domain.
In most cases, the originator address of spam emails changes every time, but the target address is frequently used.
So with this functionality, I could drop out invalid recipient addresses, without giving up the setup to use catchall all emails <everything>@your-domain.
This is useful to register webshops or community everytime using a separate target email address to distinguish incoming email if they are valid or not.
One workaround I've found is creating a mailbox without any storage, and adding any addresses to be blacklisted as aliases, but the drawback is that that way, mails can only be blackholed, i.e. the SMTP server technically still accepts the mail (so from the sender's point of view it looks like a successful delivery) before then immediately throwing it away.
It would indeed be nicer if addresses could be properly blacklisted, so that the SMTP server outright rejects any mail delivered to that address.