Outlook 365 MUA produces dovecot changing filename on some mailbox

[Emilio Augusto Lazo Zaia]

Hello

I have a setup on which dovecot is the server in a domain on which mailboxes are >20GB, some of them are 150GB or more.

When reconfiguring _some_ mailboxes with Outlook 365 (configuring a previously used mailbox on a new PC), the process takes too long even if mail visibility on Outlook is 3 months.

Inspecting at INBOX cur directory I did note that the 'ls' command shows the last file listed is a file from year 2020, 2019 or whatever not being the last received mail; that means the alphabetical ordering of 'ls' is showing past years after the last received mail, i.e. dovecot changed the epoch in filename. This only happens with Outlook. Following is an excerpt of ls:

-rw-r--r-- 1 coord.ventas ventas   544765 sep  9 10:57 1662769412.M329925P1259441.xyz.com,S=544765,W=552045:2,
-rw-r--r-- 1 coord.ventas ventas   163491 sep  5 12:14 1662769412.M74257P1259441.xyz.com,S=163491,W=165846:2,S
-rw-r--r-- 1 coord.ventas ventas  3043536 sep  9 12:02 1662769412.M777084P1259441.xyz.com,S=3043536,W=3083246:2,
-rw-r--r-- 1 coord.ventas ventas   161002 feb 27  2020 1662874173.M608062P1282222.xyz.com,S=161002,W=163373:2,S
-rw-r--r-- 1 coord.ventas ventas  2230491 feb 27  2020 1662874176.M281294P1282222.xyz.com,S=2230491,W=2259506:2,S
-rw-r--r-- 1 coord.ventas ventas   167925 feb 27  2020 1662874176.M741229P1282222.xyz.com,S=167925,W=170373:2,S

The process of renaming files is continuous until all folder was reread and renamed every file on it. If I issue 'lsof' (with grep) I see the file that is being renamed passing through tmp/ directory and after that, the file is placed under new/ directory (I guess) and Outlook sees a new email to sync, making the sync process too long... mails that have been synced are resynced...

Take a look at the timestamp on filenames: 1662769412 corresponds to "Fri Sep  9 20:23:32 -04 2022" and 1662874176 corresponds to Sun Sep 11 01:29:36 -04 2022 but mails were neither sent nor received on that dates.

What is Outlook requesting imap server to do and how to avoid this?

Thanks

-- 

Emilio Augusto Lazo Zaia
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://dovecot.org/pipermail/dovecot/attachments/20220911/24fa5f96/attachment.htm>