Can I send campaigns from a different 'From' or alias email address?
Each MailMerge365 license is associated with a single mailbox. Campaigns sent from a licensed mailbox will always be sent from the email address associated with that mailbox.
You cannot "Send As" a different email address (even if you have the Outlook permissions to do so) because of the way campaign sending works. This means you cannot simply change the "From" address of your outgoing message. If you try to send a message from a different email address than the one associated with your mailbox you will receive an error.