Over Quota Reply Codes

[dovecot at ptld.com]

Dovecot quota plugin returns code 554 5.2.2 when a user inbox is full.

Why 554 (transaction failed) instead of 552 (exceeded storage 
allocation)? Im curious behind the logic as im trying to determine the 
best code to use to reject a user sending more emails than their 
number-of-emails-limit quota.


If anyone has an option to share on the best code to return it would be 
appreciated;

    550 (policy reasons)
    552 (exceeded ... allocation)
    554 (transaction failed)

    5.2.2 (mailbox full)
    5.5.3 (Too many recipients)
    5.7.0 (Other security related)
    5.7.1 (delivery not authorized)

Which fits best?