Outlook 365 MUA produces dovecot changing filename on some mailbox

[John Stoffel]

>>>>> "Emilio" == Emilio Augusto Lazo Zaia <emiliolazozaia at gmail.com> writes:

> 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.

It looks like you're using Maildir format?  In any case, please post
more details of your configuration.  

> 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.

So the outlook client can't download and parse the number of messages
on there without breaking?  How many messages are there?  It's
probably not the size of the mailbox, but the number of messages.  

> 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:

Sure, 'ls -l' doesn't do any sorting, it just reads the directory
information as returned from the disk and show you the results.  If
you want it by time, you need to do:

    ls -ltr

to have the newest files be at the end.  But how 'ls' sees the
directry entries doen't matter to dovecot.  


> -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...

Wait what?  Can you explain exactly what you're doing here?  Why would
O365 client be renaming the file  

> 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?

What is the outlook client version?  What are your connection
settings?  Have you looked in the logs on the dovecot server side to
see what they say?  

What working clients are your users using today?  Are they working
properly with older clients?  

Basically, you have to assume we know nothing and explain your setup
and configuration to us like we're idiots who don't know anything.
Spell out all the details please.  :-)

John