Some mails seen only via POP3 but not via IMAP

[Nikolaos Milas]

Hello,

We are using dovecot-2.2.18 on CentOS 5 (with Postfix 2.11.6).

There is a usercomplaining that some incoming mails never show up in 
webmail (we are using squirrelmail - the user is checking for mail 
regularly and is not ignorant) and can only be seen/downloaded through a 
mail client via POP3 (the user uses "Leave on Server" option).

Has anyone seen such a behavior? Can you suggest some troubleshooting 
steps or solution?

What may cause some mails to not show in webmail - (or in general to 
mails accessed via IMAP, as I interpret it)?

Here is a description of user's mail directory (I have modified real 
server name and real user name):

[root at vmail ~]# tree -a /home/vmail/userx/Maildir
/home/vmail/userx/Maildir
|-- .Drafts
|   |-- cur
|   |   `-- 1291495293.M455532P28446.mail.example.com,S=2016,W=2060:2,DS
|   |-- dovecot-uidlist
|   |-- dovecot.index.cache
|   |-- dovecot.index.log
|   |-- maildirfolder
|   |-- new
|   `-- tmp
|-- .INBOX.Drafts
|   |-- cur
|   |   `-- 1317985345.M717332P17981.mail.example.com,S=1256,W=1298:2,S
|   |-- dovecot-uidlist
|   |-- dovecot.index.cache
|   |-- dovecot.index.log
|   |-- maildirfolder
|   |-- new
|   `-- tmp
|-- .INBOX.Sent
|   |-- cur
|   |   |-- 1303148518.M786490P28055.mail.example.com,S=383974,W=388998:2,S
|   |   |-- <many similar files follow here>
|   |   `-- 1458641247.M780515P22153.mail.example.com,S=2778,W=2888:2,S
|   |-- dovecot-uidlist
|   |-- dovecot.index
|   |-- dovecot.index.cache
|   |-- dovecot.index.log
|   |-- maildirfolder
|   |-- new
|   `-- tmp
|-- .INBOX.Trash
|   |-- cur
|   |   |-- 1455084995.M236797P27939.mail.example.com,S=39655,W=40327:2,S
|   |   |-- 1455084996.M373621P27992.mail.example.com,S=94946,W=97005:2,S
|   |   |-- 1455690687.M743447P11583.mail.example.com,S=109210,W=111694:2,S
|   |   |-- 1456121828.M32979P25956.mail.example.com,S=174894,W=178527:2,S
|   |   `-- 1456366474.M522472P27380.mail.example.com,S=20063,W=20335:2,S
|   |-- dovecot-uidlist
|   |-- dovecot.index.cache
|   |-- dovecot.index.log
|   |-- maildirfolder
|   |-- new
|   |   |-- 1449469045.M142541P26276.mail.example.com,S=118084,W=120599
|   |   |-- 1449814602.M29713P24846.mail.example.com,S=113968,W=116461
|   |   |-- 1450678606.M352804P11212.mail.example.com,S=191359,W=195422
|   |   |-- 1451034941.M878471P18927.mail.example.com,S=77701,W=79419
|   |   |-- 1451097359.M319601P27933.mail.example.com,S=117288,W=119151
|   |   |-- 1451459809.M54788P7084.mail.example.com,S=134906,W=137765
|   |   |-- 1453702659.M398592P1919.mail.example.com,S=142222,W=145237
|   |   `-- 1455441375.M222594P8728.mail.example.com,S=72778,W=74381
|   `-- tmp
|-- .Sent
|   |-- cur
|   |   |-- 1291025141.M538922P4661.mail.example.com,S=428,W=440:2,S
|   |   `-- 1291028972.M219139P6461.mail.example.com,S=678,W=703:2,S
|   |-- dovecot-uidlist
|   |-- dovecot.index.cache
|   |-- dovecot.index.log
|   |-- maildirfolder
|   |-- new
|   `-- tmp
|-- .Trash
|   |-- cur
|   |-- dovecot-uidlist
|   |-- dovecot.index.cache
|   |-- dovecot.index.log
|   |-- maildirfolder
|   |-- new
|   `-- tmp
|-- cur
|   |-- 1457129096.M348209P26766.mail.example.com,S=146633,W=148587:2,S
|   |-- <many similar files follow here>
|   `-- 1458901831.M100577P22147.mail.example.com,S=2439,W=2485:2,S
|-- dovecot-keywords
|-- dovecot-uidlist
|-- dovecot-uidvalidity
|-- dovecot-uidvalidity.4cf379b0
|-- dovecot-uidvalidity.53347527
|-- dovecot.index
|-- dovecot.index.cache
|-- dovecot.index.log
|-- dovecot.index.thread
|-- dovecot.mailbox.log
|-- maildirfolder
|-- maildirsize
|-- new
|-- subscriptions
`-- tmp

27 directories, 468 files


Some additional info:

[root at mail ~]# doveadm quota get -u userx
Quota name Type     Value   Limit     %
User quota STORAGE 274366 5242880     5
User quota MESSAGE    430       -     0

Thanks in advance,
Nick