Outlook 365 application error 1001, mail is not syncing

Anonymous

Good day

Having an issue with outlook 365 application on Windows 10 PC with error 1001 and the inbox is not syncing. Please could someone let me know why this is, I have tried looking online but can't seem to find much information on this error. What I found is possible issue with not enough memory but when I run task manager there is no issue with performance, memory at about 50%. When I login to Webmail, emails are working fine, so seems to be mailbox/application issue.

workforce45 631 Reputation points

2022-12-28T18:45:34.79+00:00

Hi BradleyWilson-8905,

Are you using a Microsoft authenticator or two step authentication for your Microsoft Applications/Outlook?

On the other hand, if we use a third party security software in our machine, that may interfere in software algorithms and performance.

Please update with your findings!
Yuki Sun-MSFT 41,146 Reputation points Microsoft Vendor

2023-01-02T07:51:45.52+00:00

Hi @Anonymous ,

Just checking to see if there are any updates. Did you get a chance to check the suggestions provided.
Francesco Porta 30 Reputation points

2023-09-04T12:24:22.33+00:00

i solved only deleting a windows registry key:
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity\Identities

then i rebooted the pc and after the logon always works fine.
OG-ACS 10 Reputation points

2023-09-14T03:06:29.2866667+00:00

I had this issue as well in a terminal server environment. I did cleanups of HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity\Identities , C:\Usersyourusername\AppData\Local\Microsoft\ OneAuth and IdentityCache folders

this did not resolve the issue, Contacted MS support and thy just said to blow away the user profile, this resolved the issue. kind of sad the problem had to bit with such a large stick.
Matthieu CRIBIER 0 Reputation points

2023-10-05T09:39:03.8066667+00:00

OK for me, thanks !
Dominic Kägi 5 Reputation points

2024-07-23T11:55:05.55+00:00

Had the exact same issue. None of these steps helped me.

Situation: We've got 3 terminalserver and only two of them were in use.

"Workaround": I have registered the faulty Outlook user on the second empty terminal server. After only this user was logged on to this server, I started the online repair of Office. For whatever reason, this solution or workaround worked.

14 answers

Ian Shearman 115 Reputation points

2023-06-01T16:59:16.69+00:00
I found my solution for this issue.

Close all Microsoft applications, office, teams etc.

Go to your AppData folder and navigate to Microsoft (C:\Users*yourusername*\AppData\Local\Microsoft)

Cut/paste the OneAuth and IdentityCache folders out of the Microsoft folder and paste it onto your desktop.

Relaunch Outlook and sign in. It might already be fixed at this point. If not, close out of Outlook, copy the OneAuth and IdentityCache folders back into the Microsoft AppData folder but.. when it asks if you want to overwrite, say NO.

Relaunch Outlook and sign in, should be working now.
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23 people found this answer helpful.
Cleyman Jan 0 Reputation points

2023-06-21T06:49:48.15+00:00

Thanks for the solution, problem solved !

HP 0 Reputation points

2023-06-22T11:57:36.5333333+00:00

This worked for us. Thank you for the solution.

29959021 0 Reputation points

2023-07-03T17:51:12.8+00:00

This worked for me.

Jesus Cartaya 0 Reputation points

2023-08-04T02:55:29.14+00:00

It works perfectly, thanks!

Nastaran Seifollahi 0 Reputation points

2023-09-13T07:04:48.9233333+00:00

it worked! thank you! :)

Bassam Al Dana 0 Reputation points

2023-09-26T20:41:10.46+00:00

Thank you for the solution.

Ricardo Lopes 0 Reputation points

2023-10-31T19:10:38.64+00:00

Thank you very much for the solution Ian Sherman! It worked like a charm!

kudos

Ed 0 Reputation points

2024-02-14T18:34:50.21+00:00

Just need to delete those 2 folders and have them sign back in..
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Sysarrow 31 Reputation points

2023-01-23T12:54:57.6866667+00:00

Hi, I have a same problem and the solution is restore appx profile.

I atachedd script
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4 people found this answer helpful.
Brian Healey 0 Reputation points

2023-03-06T18:18:48.4533333+00:00

Can you add it with a bitmap and use Text?

Thanks

Ine Dalberg 0 Reputation points

2023-04-18T13:01:26.83+00:00

Is there a way to do this manually? Running it as script didn't quite work for me

Sysarrow 31 Reputation points

2023-09-13T07:16:11.6033333+00:00

$Appsusers=Get-ChildItem HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Appx\AppxAllUserStore\ foreach($Appsuser in $Appsusers){ if ($Appsuser.Name -match "S-") { Remove-Item $Appsuser.PSPath } }

JohnNeu 25 Reputation points

2023-09-26T12:41:04.47+00:00

To Ine Dalbert: Here is how to manually do what Sarrow suggested:

First, be careful messing around with the registry. You can seriously mess your operating system up. Please don't get curious and start changing things on your own without solid guidance.

Logon to the PC or Remote Desktop Server (RDS/RDP) where your user is having this issue.
Tap Windows, type in CMD, right-click CMD > choose Run as Administrator > in the cmd console window type in REGEDIT and hit enter.
Now navigate to where user Sysarrow stated: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Appx\AppxAllUserStore\
Sarrow's script states that, for each directory starting with "S-", you highlight the folder and tap delete and choose Yes to delete the key and its subkeys.

I rather suggest that you RIGHT-CLICK and RENAME each S- key by appending it with "--delete20231010perIneDalbert" with that date being a future date of perhaps 1 week into the future, so that way if things become even worse with this Sarrow's hack, then you can just rename those "--delete..perIneDalbert" folders back to their original names and hopefully your situation will go back to what it was previously.

The renaming also helps your fellow administrators to see that you changed keys and/or values.

The renaming also gives allows you to search in the future for "perIneDalbert" to see just what stuff you altered. This can come in handy for later catching up on your notes (we admins often have to rush through hacks and fail to keep good notes of change attempts we made due to our being under intense pressure to get users working as fast as possible).

The renaming also help you later find those old keys & values for later deletion after you find the hack actually solved your issue.

John!
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Odysseas Tsakiridis 20 Reputation points

2023-04-25T10:33:27.6566667+00:00

Hi, I have a same problem and this is my solution that works to me:
Sign out from Office, not only from Outlook.
Sign out the mail account from Windows (Go to settings window, Click on "Accounts", Click on "Access work or school",This should show a window where you can select your account and click disconnect)
Change your account password
Rename your PC Name Restart and check again.
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4 people found this answer helpful.
Kurt Hammond 0 Reputation points

2023-04-26T16:13:43.12+00:00

Thank you Odysseas, this exact solution worked. I had tried other solutions above like running that script / manually deleting the path key's in appsx in in the registry, deleting caches of the 365 programs, disabling proxy and selecting automatic in internet options, disabling MFA, even a full reinstall of 365 did not work as well as deleting credentials in credential manager.

Lawrence Ooi 0 Reputation points

2023-06-09T01:57:02.8933333+00:00

i use the same way to handle the error, and it worked for my account.

Solution:

Sign out the mail account from Windows (Go to settings window, Click on "Accounts", Click on "Access work or school",This should show a window where you can select your account and click disconnect)

Change your account password

Rename your PC Name Restart and check again.

Alexis Joseph Betco 0 Reputation points

2023-09-05T03:07:45.8333333+00:00

Thank you. This solution works for me!
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Digital Tips 10 Reputation points

2023-03-18T15:40:17.93+00:00

I have given a similar answer on the blog : http://digital-tipss.com/2023/03/18/outlook-365-application-error-1001-mail-is-not-syncing/
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2 people found this answer helpful.

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Dr N B Shridhar, Professor and Head,VPT 5 Reputation points

2024-04-03T13:53:01.7733333+00:00

Any of the steps arenot useful and microsoft people will not help. Uninstall windows and reinstall
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Outlook 365 application error 1001, mail is not syncing

14 answers

Just need to delete those 2 folders and have them sign back in..

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