Can these logs help ?
Aug 03 23:33:32 auth(default): Info: client out: OK 1 user=postmaster@shc.gov.pk
Aug 03 23:33:32 auth-worker(default): Info: sql(postmaster@shc.gov.pk,127.0.0.1): SELECT CONCAT(mailbox.storagebasedirectory, '/', mailbox.storagenode, '/', mailbox.maildir) AS home, CONCAT('*:bytes=', mailbox.quota*1048576) AS quota_rule FROM mailbox,domain WHERE mailbox.username='postmaster@shc.gov.pk' AND mailbox.domain='shc.gov.pk' AND mailbox.`enableimapsecured`=1 AND mailbox.domain=domain.domain AND domain.backupmx=0 AND domain.active=1 AND mailbox.active=1
Aug 03 23:33:32 auth(default): Info: master out: USER 19 postmaster@shc.gov.pk home=/var/vmail/vmail1/shc.gov.pk/p/o/s/postmaster-2013.02.23.06.02.05/ quota_rule=*:bytes=419430400
Aug 03 23:33:32 imap-login: Info: Login: user=<postmaster@shc.gov.pk>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, secured
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: Loading modules from directory: /usr/lib64/dovecot/imap
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: Module loaded: /usr/lib64/dovecot/imap/lib10_quota_plugin.so
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: Module loaded: /usr/lib64/dovecot/imap/lib11_imap_quota_plugin.so
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: Module loaded: /usr/lib64/dovecot/imap/lib20_autocreate_plugin.so
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: Effective uid=501, gid=501, home=/var/vmail/vmail1/shc.gov.pk/p/o/s/postmaster-2013.02.23.06.02.05/
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: Quota root: name=user backend=dict args=:proxy::quotadict
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: Quota rule: root=user mailbox=* bytes=419430400 messages=0
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: Quota warning: bytes=356515840 (85%) messages=0 command=/usr/local/bin/dovecot-quota-warning.sh 85
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: Quota warning: bytes=377487360 (90%) messages=0 command=/usr/local/bin/dovecot-quota-warning.sh 90
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: Quota warning: bytes=398458880 (95%) messages=0 command=/usr/local/bin/dovecot-quota-warning.sh 95
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: dict quota: user=postmaster@shc.gov.pk, uri=proxy::quotadict, noenforcing=0
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: Namespace: type=private, prefix=, sep=/, inbox=yes, hidden=no, list=yes, subscriptions=yes
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: maildir: data=//var/vmail/vmail1/shc.gov.pk/p/o/s/postmaster-2013.02.23.06.02.05//Maildir/:INDEX=//var/vmail/vmail1/shc.gov.pk/p/o/s/postmaster-2013.02.23.06.02.05//Maildir/
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: maildir++: root=//var/vmail/vmail1/shc.gov.pk/p/o/s/postmaster-2013.02.23.06.02.05//Maildir, index=, control=, inbox=//var/vmail/vmail1/shc.gov.pk/p/o/s/postmaster-2013.02.23.06.02.05//Maildir
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: Namespace: type=shared, prefix=Shared/%u/, sep=/, inbox=no, hidden=no, list=children, subscriptions=yes
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: shared: root=, index=, control=, inbox=
Aug 03 23:33:32 IMAP(postmaster@shc.gov.pk): Info: Namespace : Using permissions from //var/vmail/vmail1/shc.gov.pk/p/o/s/postmaster-2013.02.23.06.02.05//Maildir: mode=0700 gid=-1
Aug 03 23:33:33 IMAP(postmaster@shc.gov.pk): Info: Disconnected: Logged out bytes=337/502881
