Log in to the Microsoft 365 Admin center portal https://admin.microsoft.com
In the left pane, click Exchange under the Admin section.
Click Mail flow.
Under the rules tab, click the + button and click Create a new rule.
The transport rule window will be displayed.
In the Name field, enter Thread Mail Flow.
For Apply this rule if, click The sender is external/internal and choose – Outside the organisation.
(In-house legal teams may want to skip this step, if they would like emails from other individuals within the organisation to be included in the mailflow).
Select the phrase and click 'Save'.
Under Except if… select ‘The sender... is this person’ and select the dedicated email address.
Click Next.
Once Thread is installed, log on to Thread using the Global Administrator details.
Click the Settings tab at the bottom part of your Thread panel.
Click the System tab.
Once the above steps have been completed, you can add new users to your Thread account. New users must already exist on your company’s database, have a Microsoft 365 account, and have an appropriate Microsoft 365 license.
To test that setting up the email functionality has worked:
Send an email to an individual who has been added to Thread, follow the below email content.
Subject : Thread test - Please ignore
Body of the email : This Thread Request ID is used to track application communication
The email should appear in the Unassigned Emails tab of Thread if sent successfully.