Microsoft 365 Admin - Add Mailboxes

Go to Exchange Admin Center

Select the SigParser Mailboxes Mail Enabled Security Group

Select Members

Select View and manage members > Add members

Add the mailboxes you want to connect to SigParser

In SigParser, go to Mailboxes > under the "Connection" column, select the Office 365 Admin Connection

Select the Resync button at the top of this page

You should see the mailboxes added at the bottom of the page.