From:  Tanstaafl <tanstaafl@libertytrek.org>
Date:  11 Apr 2019 21:02:43 Hong Kong Time
Newsgroup:  news.mozilla.org/mozilla.dev.apps.thunderbird
Subject:  

Re: EXTREMELY slow IMAP --> outlook.office365.com SINCE ~March 1 ....

NNTP-Posting-Host:  63.245.210.105

On Wed Apr 10 2019 21:17:29 GMT-0400 (Eastern Standard Time),
richpindertalk@gmail.com  wrote:
> Thanks Jorg & Tanstaafl... [i thought I posted this earlier...didnt go thru]
> 
> been using 993 + ssl/tls for years now
> 
> version - current: 60.6.1;  Think the 60.5.x group worked fine.....

I'm on 60.6.1 and it is working fine with 8 Office 365 accounts (all
IMAP), so I don't think the version is the problem.

> ALSO - one other tidbit... I have a TBird install, same platform, same TBird version, using IMAP - but NOT to O365 (it connects to my wife's justemail.net server:  WORKS PERFECT, no lag, no messages saying  'Not Responding' !

Maybe a profile issue - I can't remember, have you tried a clean profile?

> Thanks in advance for your thoughts !

The only other things I can think of are ...

Antivirus interfering (if you are scanning in/outbound email, don't)?

Check your offline settings - are you using GLODA? Is it trying to Sync
GBs of email?