My question is, if after doing all the patter matching and deciding what to do with the message maildrop realises that it can't deliver to the maildir because the quota is over. Then it exits with 77 (as the documentations says) and so vdelivermail passes the failure back to qmail and so on and the message is bounced back to the sender with whatever output error given by maildrop. In this case the message "quota is over".

The problem is, a lot of these messages that are bounced because of quota are actually spam and could have been dropped instead and also the error message that is bounced back to the sender is not descriptive enough for many non-technical and/or non-english speaking people.

Is there any way to write a statement in the .mailfilter that catchs the over-quota exit code or understand that the user is over quota. So I could add more conditions based on whether the message will be delivered or not, or even dropped if its spam score is too high.