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Outlook 2019 / Microsoft 365 - IMAP Email Account Stopped Functioning

Microsoft Outlook stores data in .PST and .OST files with a maximum file size of 50GB.

Please ensure that you have enough disk space on your computer for at least 50GB.

Performance degradation occurs at 12GB or roughly 12,000 messages in a single folder.

We recommend keeping your Inbox clean by creating folders and moving messages you do not need to those folders.

Outlook will run optimally with an Inbox size of 4GB or less and approximately less than 1,000 messages.

Sometimes PST and OST files can become corrupt causing Outlook to stop functioning.

This tutorial will show you how to reset Outlook 2019 / Microsoft 365.


Step 1: If you have Calendar appointments, Contacts, and/or Tasks, you need to back them up first.
Go to File


Step 2: Select Open & Export from the left menu
Click Import/Export


Step 3: Select Export to a file
Click Next


Step 4: Click Next


Step 5: Select Calendar (or Contacts or Tasks)
Click Next


Step 6: Click Browse


Step 7: Name the file Calendar (or Contacts or Tasks)
The file will be saved in your Documents folder
Click OK


Step 8: Click Next


Step 9: Click Finish


Step 10: Set a date range
Click OK


Step 11: Repeat steps 1-10 for Contacts and Tasks


Step 12: Close Outlook


Step 13: Open the Control Panel in Windows
Select View by: Large icons on the top right dropdown
Click on Mail


Step 14: Click Show Profiles...


Step 15: Click Remove


Step 16: Click Yes


Step 17: Click Add


Step 18: Name the profile EnGuard
Click OK


Step 19: Fill in the following details.
A) Enter your name, this will be the displayed on all outgoing messages (what recipients see)
B) Enter your email address
C) Enter your password twice
Click Next


Step 20: Check the box for Change account settings
Click Next


Step 21: Click More Settings ...


Step 22: Go into the Advanced tab
Set Outgoing server (SMTP) to port: 587
Select STARTTLS from the Use the following type of encrypted connection dropdown
Click OK


Step 23: Click Finish


Step 24: Click Close


Step 25: Click OK


Step 26: You will now import your Calendar, Contacts, and/or Tasks back into Outlook
Open Outlook
Go to File


Step 27: Click Import/Export


Step 28: Select Import from another program or file
Click Next


Step 29: Click Next


Step 30: Click Browse and select the Calendar file you saved earlier (or Contacts or Tasks)
Click Next


Step 31: Select Calendar (or Contacts or Tasks)
Click Next


Step 32: Click Finish


Step 33: Repeat steps 26-32 for Contacts and Tasks