Getting 2400 error in outlook application

Good morning (UK)

I'm back up working all OK today.

Last night, I did an Online Repair (from Control Panel) of the entire M365 suite but didn't have time to test the result.

So, either that fixed it or something else has happened overnight. Anyway, I hope it's a way forward for those of you who have the ability / permissions to try this.

Good luck.

Not fixed for me. Also removing the account and re-adding it doesn't change anything. Error 2400 remains

I have the exact same issue..

I can tell you what I did to resolve this - and some of the annoyances. Please excuse the roughness of these notes, I'm doing this in transit and am super busy. Normally I wouldn't post something this disorganized. You can skip to the bottom, but the intermediate stuff MIGHT be of interest

Many obstacles surprised me here - and a bunch of old registry notes on outlook I'd made over the years were useless. Granted I haven't had issues in a while.

Firstly - OS is Windows 10/64 Pro 22H2

This did NOT occur on any of my Windows 11 Machines (I did the update on those AFTER I dealt with this mess on my couch clunker - 3-4 hours after, so the update package was likely identical )

I have several mail accounts - two outlook.com, a couple of gmail and my own servers.

I only had a problem with ONE of the outlook accounts. The free one. (other is attached to 365)

I had multiple backup/restore methods set, but 2FA on that account was OFF.

I turned 2FA on - tried resetting the account via outlook FILE/Account settings and via the CP applet - manually. DID NOT WORK.

I tried getting APP passwords - and was even prompted to do so. They ALWAYS failed and I had to use the main PW for the account.

(this indicates to me that SOME authentication is occurring - it rejected the app password, seemed to accept my main PW, but then failed, so....)

I tried removing just that account.... but - these days MS doesn't like that EVEN when I've moved default send/datafile to another account (this is not because of 365 - I use the free account as default datafile for calendar/contacts for reasons to bizarre to explain here - hehe)

In fact I had a real issue removing the Outlook accounts in general - which is strange... I don't do it often, but I used to do it regularly...anyway...

Once I removed them all, I added them in again - HOWEVER I noticed I wasn't being asked for credentials.... so there was some residual BS in the registry. I continued, but THAT FAILED TOO

I removed the profile - which doesn't actually remove the profile.... and it won't let you recreate a profile with the same name. because of that (it just flicks a flag somewhere in the registry - I was too impatient to figure out where the specific flag is ....but this annoys my OCD).

I deleted the profile from the registry. This allowed me to create a new profile with the same name BUT it did not fix the problem.

This is the location of the profiles FOR REFERENCE

• PLEASE DO NOT MESS WITH THE REGISTRY if you don't know what you are doing..... EVER.... seriously.... at least export the profile key

HKCU\SOFTWARE\Microsoft\Office\16.0\Outlook\Profiles

I ended up completely removing Office and reinstalling. Yes, completely.... I HATE doing that.

FYI all the PINNED lists etc in the other apps remained... this was expected, but nice to know (this ASSUMES you are using MS365 of course - and it SYNCS)

Of course - as we all know - restart after uninstall and again after reinstall - THEN do the accounts.

AND - while I always express caution with the registry - so I am NOT advising this - after the uninstall and before the restart, I deleted the ENTIRE 16.0 key in the registry.

(I can't say if the registry bit helped - and I didn't go through every other location related to office in the registry - or touch the older office keys)

I hate doing RE&RE - always the last resort for me.... but....

Typically I prefer to isolate the specific flaw. This is a brute force repair which I personally consider extremely shoddy work.

NO guarantee this will work for everybody/anybody

Again, sorry for this mess of a ramble - I'm doing this from recall - on a plane... surrounded by the new class of travelers that demand every wish and absurdity be met - TickTock twerps ..... hehe...

Cheers

UPDATE: Without doing anything at all, the @outlook.com email address account became functional again on my PC overnight! MS must have made another update to correct as I updated again over the weekend. What a pain in the **** this has been, though. Hope everyone else has this luck, too.