Can I send campaigns from a different 'From' or alias email address or using multiple accounts or shared mailbox?
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.
Shared mailboxes are not supported due to a technical limitation. If you turn a shared mailbox into a regular mailbox with a full Microsoft 365 you can login as that mailbox and use MailMerge365.
Please use the trial to test if your use case works.