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