Geting mail quota exceeded with plenty of space

I have a user that is getting mail quota exceeded:

Feb 9 15:00:21 z9m9z dovecot: lda(dm@htt-consult.com): Error: sieve: msgid=38308773.1704736628308773ywdm@htt-consult.com853430: failed to store into mailbox 'INBOX': Quota exceeded (mailbox for user is full)

Yet the quota is set for 1000Mb and the current reported use is 277Mb.

There are only 28 messages in the in box and 842 in the spam.

Where might the problem becoming from?

The server is Redsleeve 6 (Centos6 on arm). I am running a combination of postfix/dovecot/roundcubemail with a mysql virtual domain database maintained with postfix.admin