Secondary addresses in Microsoft 365 channels work (almost) just like they do in email channels, so this article is lifted (almost) verbatim from here.
Secondary addresses (also known as aliases) allow you to send emails with a different “From:” address from the one on the account.
👀 Secondary addresses must be added to your Microsoft account first.
- Personal accounts
- Hosted Exchange accounts
In your Exchange admin center:
select a user under recipients > mailboxes,
edit it (double-click or ✏️), and
add an an alias under email address.
Contact your administrator if you don’t have access to an admin account.
Your email provider may also be set up to receive incoming messages for many addresses in the same mailbox. If this is the case, be sure to add your alternate inbox addresses here.
- Display Name
The display name used for outgoing email.
Email display names value can be further customized in the Settings tab.
The alias address to send outgoing messages as.
The email account to be used when sending outgoing messages from this alias.
Optional. Only visible from this dialog, the REST API, and the Rails console.