Error similar to this when opening Outlook:

Office 365 and Exchange accounts use an Offline Storage Table (.ost) file to store a synchronised copy of the mailbox information on the local computer, there can be multiple reasons for file corruption such as Outlook add-ins, synchronisation error, storage limitations

Solution 1: Repair using Outlook inbox repair tool

1. Exit Outlook

2. Open File Explorer (Ctrl + E)

3. Navigate to: C:\Program Files (x86)\Microsoft Office\root\Office16

4. Run Scanpst.exe

5. If the file name isn't picked up automatically select browse and find the file C:\Users\{username}\AppData\Local\Microsoft\Outlook\{UPN}.ost

6. Press Start

7. Select "Make backup of scanned file before repairing", then press Repair

8. Press OK then open Outlook to confirm file is repaired

If this doesn't fix it follow the steps below:

Solution 2: Creating OST File Again

1. Exit Outlook

2. Open File Explorer (Win + E)

3. Navigate to C:\Users\{username}\AppData\Local\Microsoft\Outlook (Note: AppData is a hidden folder, need to enable hidden folders or put AppData directly into address bar)

4. Right click on the file {UPN}.ost and rename to {UPN}.ost.old

5. Re-open Outlook which will re-create the .ost file

Solution 3: Create new Profile

If neither of the above options do not work we can try creating a new profile:

1. Open Control Panel

2. Navigate to User accounts > Mail (Microsoft Outlook 2016) (32-bit)

3. Select Show Profiles

4. Select Add

5. Enter a name and press OK

6. Allow around 10 seconds to auto discover the email address, otherwise select manual setup and enter email details

7. De-select Setup Outlook Mobile on my phone, too and then press Finish

8. Change the default profile to the Profile we just created