[Dovecot] Dovecot generate file when over quota detected

[Dominic Malolepszy]

Hi,

I am curious if Dovecot can add an empty file into a Maildir folder as 
soon as a mailbox has exceeded 100% capacity, and later when it detects 
the quota has fallen below 100% unlink the file. The idea is the Dovecot 
LDA would deliver the message and if this caused the mailbox to reach 
100%+, add a file into the maibox say "username/Maildir/overquota". 
Interactions via Dovecot IMAP/POP3 that lower the mailbox usage, for 
example the user popping, or deleting mail from the mailbox would 
trigger Dovecot to unlink the file.

This means that an MTA can efficiently check for the existence of this 
'overquota' file and return a "user at domain.com Mailbox full" TEMPFAIL 
error early during the SMTP transaction prior to accepting any data.

Dominic