Thought I would share a piece of useful information regarding the use “other emails” in Exchange online. Traditionally, an account is created with an email address for handling public and shared email accounts. In Office 365, you can add “other emails” to an account to save the cost of adding additional accounts. In order to identify the emails coming in from the difference email addresses, you can use a server rule looking into the internet header information.
In my case, the email I am looking for is firstname.lastname@example.org. I created a new blank rule and use the condition “with <specific words> in the message header”. Then you can create whatever action is deemed proper.