Outlook 365 application error 1001, mail is not syncing - Microsoft Q&A
Dear Caroline Dang,
As your request here are some possible solutions that would fix your issue:
1.Repair Office 365 app.
Go to control Panel-> Uninstall a program-> Choose Microsoft O365 -> right click-> change-> repair -> you can see Online Repair and Quick repair options.
you can choose 1 option to repair the application.
2.Create new Outlook profile.
Go to control Panel->On the top right and change "view by" to small icon-> Click on "Mail (Microsoft Outlook)
Show profiles->Click add -> choose a name for your profile -> Choose the Email Account option -> Usually it will already prepare the email address for you, if it not please helps me to enter your account there->Click next->finish->now you will see a new profile in the Mail tab->
For this example, in my mail tab, I create a new profile name "d" and please help me to follow this picture and set the profile as " Alway use this profile."
3.Delete user credentials.
Go to control panel like solution 2 -> Credential manager-> Choose Windows credential->from the generic credential-> Find all the credential that related to "OUTLOOK" -> click that credential-> remove.
this solution will delete the credential that are saved in outlook so that you could log in and re-sign in again instead of automatically sign in.
4.From your computer search bar type "Run"-> in the run tab type "%localappdata%\Microsoft\Outlook" ->navigate to RoamCache folder-> Delete all file.
5.From your computer search bar type "Run"-> in the run tab type %localappdata% ->Go to Microsoft folder -> cut and paste "IdentityCache" and "OneAuth" Folder to your desktop -> Run outlook -> If the issue is Fixed you can delete two folder,if the issue is still present move the two folders back to where you pull them out.
If you have any issue performing these steps, please response to my email and I will get back to you as soon as possible.
Best regards,
Clover
Microsoft 365 Support Engineer
Email Address: v-llo@microsoft.com
Working Hours: Monday to Friday: 10:00 AM CDT – 06:00 PM CDT
My Team Lead: David Doan | Email: v-nhatdoan@microsoft.com
My Team Manager: My Le | Email: v-myle@microsoft.com
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