When an over-quote user receives email
This option controls what happens when a mailbox that is close to or over its
disk quota receives email that would put it over quota. By default Virtualmin
will bounce the email back to the sender - but if you select the Queue
option, email will be held in the local mail queue and re-tried at regular
intervals.
If the user's disk usage eventually drops below quota, the message will be
delivered. However, if usage never drops the message will be bounced back to
the sender after a period configured by the mail server (typically 5 days).