IMAP tuning for Outlook 365

[Paul Kudla]

Ok sorry to NOT have an answer you are looking for but I don't want 
anyone wasting their time on what is clearly a microsoft issue.

Outlook 365 / Outlook since 2010 simply does not support imap.

You can tweek it here and there however here are the basic's

Outlook IMAP does not support IDLE thus no auto upating of the inbox and 
other folder changes etc...

Outlook (this if from experience) simply does not handle large anything 
folders well, especially imap - hence the click at the bottom of a 
folder to see more (ie history) ??

I had a customer spending 700+ / mth to telus because people were 
leaving emails behind (out of sight out of mind)

yes that was per month !

that being said the best you can do with outlook is set to auto update 
the send/receive settings to every 5 minutes or so

A 3G email box is an issue no matter what as the size is the direct 
issue of the lockups, and/or the quantity of emails in the folder

Outlook seems to work ok until about 200 emails (max 1000) in a folder 
and maybe 1G of actual data.

Yes you can move emails to other folders, but the folder will still try 
to sync in the background and will eventually lock up pending the size.

I use thunderbird and although it has its short commings, it handles 
large email boxes extremely well, handles IMAP IDLE protocol

other imap clients (apple ios mail - iphone, windows mail - the free one 
(suprised me) )

I am running 26G of email, 150+ folders etc etc (some folders aproach 
10000 emails - archived stuff) and no real issues on a replicated 
dovecot 2.3.19 server setup.

What needs to be kept in mind is that Microsoft (espically 365) is 
trying to push exchange protcol and has all but dropped support for IMAP.

Again open to comments but i recently was forced to use Outlook (Office 
365) for a customer and ran into all of these issues yet again, i am 
weeding them off of Outlook in favor of thunderbird.

FYI





Happy Tuesday !!!
Thanks - paul

Paul Kudla


Scom.ca Internet Services <http://www.scom.ca>
004-1009 Byron Street South
Whitby, Ontario - Canada
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Toronto 416.642.7266
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Fax 1.888.892.7266
Email paul at scom.ca

On 1/31/2023 10:07 AM, Artur Pydo wrote:
> Hello,
> 
> I'm looking for advices on IMAP config tuning for best user experience 
> with Outlook 365.
> I'm currently using dovecot 2.3.4.1 (f79e8e7e4) provided with Debian 10.
> One of my users has Outlook 365 and an IMAP mailbox of large size with 
> several folders (more than 3GB).
>  From time to time as his main inbox folder is growing he can see some 
> problems with its Outlook application.
> Sometimes it freezes during mailbox synchronisation, sometimes he can't 
> see new incoming emails.
> 
> I wonder if there is some specific workarounds for an up-to-date Outlook 
> in Dovecot or if you can suggests some config setup adjustments 
> (timeouts, idleing ...) to avoid problems in his Outlook.
> Most of the config are defaults. But I can provide relevant parts of the 
> config if needed.
> 
> I have this workaround activated for a long time:
> imap_client_workarounds = delay-newmail
> 
> By the way, I also have a big IMAP mailbox. Can't see any server 
> specific problem while connecting with Thunderbird to this Dovecot server.
> 
> -- 
> Best regards,
> Artur
> 
> 
> -- 
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