My email address was initially set up as firstname@domain.com.

I added an alias from the Office365 Admin Center as first.last@domain.com.

I then set first.last@domain.com as the primary alias.

I logged out and logged in with the new address and when I look at my account details it says first.last@domain.com.

However, when I send an email it still comes from firstname@domain.com.

How do I change the from field in the email so that it says first.last@domain.com?