If your Microsoft 365 account disconnected after connecting, it could be because SMTP is disabled.
Microsoft/Office 365 accounts purchased directly from Microsoft
Here are the steps to enable SMTP for Microsoft 365/Outlook accounts purchased directly from Microsoft:
Log in to your Microsoft Admin Center.
Go to Users > Active Users.
Select the user, and in the flyout that appears, select Mail.
In the Email apps section, select Manage email apps.
Check IMAP and Authenticated SMTP.
When you're finished, select Save changes.
After an hour, click on your selected account's three dots in Instantly and select Remove account
Then connect them again. Waiting for an hour is a crucial step. This allows Microsoft to propagate the changes and share new tokens with us.
Microsoft/Office 365 accounts purchased from GoDaddy
When you get Microsoft 365 accounts on GoDaddy, the setup is different for the accounts that are bought directly from Microsoft. You won't be able to access all the features in Microsoft Admin; instead, your SMTP email settings will be on GoDaddy.
You need admin permissions to manage SMTP Authentication. For more info, see admin roles from Microsoft.
Here are the steps to enable SMTP for Microsoft accounts purchased from GoDaddy. You can also watch the full video walkthrough here.
Log in to your GoDaddy account.
Navigate to My Products.
Scroll down and select the Email and Office section.
Click Manage all and find the user you want to enable SMTP for.
Select Manage next to the user.
Scroll down to Account information and select Advanced Settings.
Turn on the SMTP Authentication toggle.
Wait for an hour and connect your account to Instantly.
Note: In case you are getting the error 'Your account already exists' when trying to add it, please log in to Instantly from the Incognito window.