Outlook not syncing with 365. Connection Status Under Authn: Error

Occasional Contributor

Have only happened to a couple of users so far. Just started in the past week or two. Outlook 2016 and also Outlook 365(Perpetual) on Windows 7(so far).

Completely Nuking the outlook profile, all the entries in Credential Manager, and deleting the C:\users\user\appdata\local\Microsoft\Outlook contents and setting it back up fixes it for a while. Then the user starts noticing stuff getting stuck in outbox and e-mail not rolling in.

Made sure TLS 1.2 is blah blah blah here since the switch: https://support.microsoft.com/en-us/help/3140245/update-to-enable-tls-1-1-and-tls-1-2-as-default-sec...

Tried Online repair. Tried complete removal and upgrade from Outlook 2016 to Outlook 365 perpetual.

Checked connectivity with the online MS tool - seems fine.

Tried with and without ipv6 on on the NIC.

Tried safe mode and ditching all add-ins but Exchange.

Tenant has modern authentication active, but neither of the two users so far has two-factor enabled.

Changed both users passwords in case it was some odd case of old or expired credentials somewhere.

Have seen some reports on downdetector.com of people saying outlook won't sync only a few.

Their phones send and receive fine.

10 Replies

Yeah, it didn't really come back with anything.  (Something about checking ignored conversations)


I've just had it happen to another user.  Instead of nuking the profile, creds in cred manager, and the C:\Users\user\appdata\local\microsoft\outlook folder  as I had been doing to those affected,


Saw someone post something about it being the fault of SDXHelper.exe.  I closed outlook, killed the outlook.exe process as it was stuck, then killed two instances of SDXHelper.exe that were there.  Launched outlook, and it instantly connected and all the messages left the outbox properly and continued syncing properly.  Then, checked for office updates manually(it was already up to date).  Don't know how long it will last.


So it appears a recent update somewhere made a change to SDXHelper.exe to reach a state that prevents Outlook from syncing properly.  This has been observed on Windows 7 so far only, and with Outlook 2016 and Outlook 365 perpetual.


We'll also see if this is the case if and when the other machines exhibit the behavior again OR if other users start having it.

I can confirm we have been having this issue as well for a few weeks.  All users on ClicktoRun version of office 365.  It started after we enabled MFA on all of our user accounts recently, but even disabling MFA for a user will not fix the issue.


It's not all Windows 7 users, maybe 20%.  One thing that does seem to be consistent is that all of the users having this issue have the "New UI" in Outlook (new icons).


Killing sdxhelper.exe and restarting outlook will temporarily fix the issue , or simply rebooting, but it always comes back.  It's happening multiple times per day for some users.



We are having the same issue with Click to run Version 1810 (Build 11001.20108)


The sdxhelper.exe work around does work however it doesn't explain the cause.    What specific Version and build are you running?

Same version (16.0.11001.20108) on one I just checked, but we've seen it happen on other builds as well.  

I just updated a few clients to 1811 (Build 11029.20079)  and patched for TLS 1.1/.2


I'll post back any change in behavior.

I had the same problem from the past 2 weeks I think.
This morning I took a look at it with a finer comb and saw the SDXHelper being the culprit (ironic - its not helping anything :)) - before finding this thread.

Just also updated Office to 1811 - hopefully this will fix it.

@ahmedilyasHope all is well.  Were you able to find a solution?  Did this work for you?

@ckalexander22 - I believe after the update I did, it fixed it.