
When other accounts are added to Outlook they are considered as Secondary Account. You must remove all other Exchange account before removing the primary account. So when migrating from one Exchange service to another Outlook throws error message, ‘The primary Account cannot be removed unless it is the only account in profile. The first account added is the primary account.

You can add a Gmail account, work account in Outlook.

This feature is available in Outlook so that users can get all their emails in a single application. A user can add two or more accounts in Outlook e-mail application.
