Home > Microsoft Outlook > Outlook 2019 / Microsoft 365 - Outlook Sync Stopped Functioning

Outlook 2019 / Microsoft 365 - Outlook Sync 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 Sync to stop functioning.

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


Step 1: Close Outlook


Step 2: In Webmail, go to Settings => Connectivity => Open EWS


Step 3: Click Delete


Step 4: Click Delete


Step 5: Open Outlook (MAPI)


Step 6: Click Delete


Step 7: Click Delete


Step 8: Open the Control Panel in Windows
Select View by: Large icons on the top right dropdown
Click on Mail


Step 9: Click Show Profiles...


Step 10: Click Remove


Step 11: Click Yes


Step 12: Click Add


Step 13: Name the profile EnGuard
Click OK


Step 14: 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 15: Click Finish


Step 16: Click OK


Step 17: Open Outlook, wait for folders to update, leave it open until it only says All folders are up to date.
(May take a few hours depending on how much data you have)