Mac Mail: how to send from multiple Exchange aliases ?

Customer is using Office 365 as backend and uses several domains:,, etc.

Each user has one mailbox and assigns multiple aliases/addresses to that mailbox:,, etc. Any mail sent to any of the aliases ends up in the user's mailbox, fine.

On the client side, users are using Macs with the built-in Mac Mail application.  The users must be able to select the alias they want to use as sender's email address. How can this be achieved ?

Things tried that did not work: adding the aliases into the account preference (you can then select an address to send from, however emails always appear to come from the default address), using shared mailboxes for the additionnal email adresses and access them via IMAP (sending works but emails are downloaded multiple times, a sending only IMAP account would be nice)

Any help would be appreciated.
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I am assuming it is the "reply to" address you want to be able to change.

To do that, in Mail go to Mail > Preferences > Accounts > Account Information

In the box "E-mail address" enter all the e-mail addresses you might want to use as Reply To addresses separated by commas.

Save the preferences, then quite and restart mail.

When you compose a mail message, click on the "From" box and you should be presented with a drop-down box allowing you to select among the E-mail addresses you put into the prefs box.
xmiAuthor Commented:
I already tried that, it does not work. While I am able to select an email adress when I compose the message, it is always the first address that get's assigned as reply-to.

My assumption here is that the client does not communicate well with the Exchange BackEnd and that it is always the Office 365 / Active Directoy UPN that is used as reply-to.
You may be right. It seems to work with IMAP accounts and unfortunately, I don't have an exchange account to test.
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Will SzymkowskiSenior Solution ArchitectCommented:
You can ONLY have one Primary SMTP address. This is the only address you can send from Alias are only for receiving mail not sending.

xmiAuthor Commented:
OK, I figured it out. Let's say that a user's main address is The user has a second email address: and I want to be able, from Mac Mail, to send emails from both addresses.

On the Office 365 / Exchange backend, I create a shared mailbox whose email address is The shared mailbox has an alias that is user-company2. Emails arriving in that mailbox are automatically forwarded to the mailbox.

On Mac Mail, I have to create a new IMAP account with the following characteristics
(the Mac on which I test has not an Engish UI, so please excuse any approximative translation)

Complete Name: First Name / Last Name (Company2)
Email address:
Password : the user's Office 365 password

On the next screen:

Account Type: IMAP
Incoming server:\user-company2
Password: the user's Office 365 password

On the next screen:

SMTP server:
Password: the user's Office 365 password

In the account properties, I go to the advanced options and I disable 'include this account when retrieving emails'

When this is complete, I can select any of the two addresses to send emails. All replies do end up in the main mailbox as requested by the customer.

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xmiAuthor Commented:
Self answered the question after some testing.
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