The second argument to deliverquota is optional. If present, quota specifies a new quota setting for this maildir. Specifying quota is equivalent to running maildirmake(1) with the -q option. The second argument to deliverquota is considered obsolete, and may be removed in the future.
deliverquota reads the message from standard input and delivers it to maildir. maildir may specify a path directly to a maildir folder, not the main maildir (as long as the folder was created by the maildirmake(1) command.
The -c option automatically creates the maildir, and all missing parent subdirectories (as 'mkdir -p'). This option should be used with caution.
The -w N option places a warning message into the maildir if the maildir has a quota setting, and after the message was successfully delivered the maildir was at least N percent full. The warning message is copied verbatim from /etc/quotawarnmsg with the addition of the "Date:" and "Message-Id:" headers. The warning is repeated every 24 hours (at least), until the maildir drops below N percent full.
deliverquota delivers the message to the maildir and terminates with exit code 0 if the message can be delivered without going over quota.
If the maildir is over its specified quota, deliverquota terminates with exit code 77 (EX_NOPERM).
maildirquota(7), maildirmake(1), http://www.qmail.org/man/man5/maildir.html.