Hello, everyone.

We have recently begun migrating folks from an older server to a newer one, and things have been going quite well except for -- you guessed it -- Outlook 2010 users. Specifically it appears to be one customer in particular, and this particular customer has many nested mailboxes and lots of e-mail in general. Not sure if this is a factor.

Old server:

• Ubuntu 10.04.4 LTS
• Dovecot 2.1.13
• Maildir++
• Local auth via passwd/shadow files

New server:

• Debian GNU/Linux 8.6
• Dovecot 2.2.13
• Maildir++
• Quotas enabled
• LDAP

Basically what's happening is that users are seeing large delays when navigating between different IMAP folders. So, for example, user "X" is sitting idle in their INBOX. If they then click on another folder there's a good 6-7 second delay before you can view its contents. If you immediately then navigate to other folders, you get a rapid response. But if the client then goes idle again for 10+ seconds, you will get this delay again. Some are reporting the OS saying "Outlook is not responding." (Everyone is running Windows 7.)

Disclaimer: Yes, I know Outlook 2010 is a giant steaming pile of ____.

However, everything worked dandy with Dovecot 2.1 and of course my customer is harping on this fact.

Things I have tried/read about in the Dovecot list:

• Check headers only -- doesn't seem to help.
• Had a user completely remove their IMAP profile and re-add: no change.
• Had a user set up an entirely new account on a new computer: same symptoms.
• Someone mentioned to enable the "delay-newmail" workaround in 20-imap.conf, but this wasn't enabled in our 2.1 install, so that seems like it would not help our case.

I was looking through the release notes of later Dovecots, and I noticed that in 2.2.14 there's mention of some issues with Outlook that were fixed, but it wasn't particularly specific about which versions. Should I be looking into that? And if so, is there a separate repository for newer dovecot? Currently the standard Debian 8.6 only has 2.2.13.

Any help, suggestions, or pointers would be greatly appreciated. Thank you!

		- bryan