[Dbmail] Question on the max mailboxsize setting

[Jacques Dimanche Test]

After setting up the dbmail to work with sendmail, I can receive email 
messages just fine in pop3 and imap.  Playing around with the user 
settings, I wanted to change my mailbox size to a lower limit to see 
what happens when I exceed my limit.   After making the change, in such 
that I have actually exceeded my mailbox size, I tried to send myself a 
limit and got the following error:

Oct 21 01:02:52 localhost sendmail[4271]: i9KH2q27004269: 
to=<[EMAIL PROTECTED]>, ctladdr=<[EMAIL PROTECTED]> (0/0), 
delay=00:00:00, xdelay=00:00:00, mailer=dbmail, pri=30307, 
relay=home.sysads.com, dsn=4.0.0, stat=Deferred: dbmail mailer 
(/usr/local/sbin/dbmail-smtp) exited with EX_TEMPFAIL

Is the above normal behavior?  That all incoming messages that exceed 
mailbox size is just accepted until the mailer decides to give up on it 
and send it back?  Reason I ask, is that in a large user environment, 
such as an ISP, this could lead to a large queue of messages that will 
be processed every 15 minutes (or however you have your queue check 
interval set at) until space either frees up or how long you have your 
hold time before bouncing the message back.

Is it possible to bounce it back right away with a simple message 
stating that the user's mailbox size has been exceeded and that the 
message is undeliverable?