Configure your main Exchange as an Exchange account in order to have all other associated services such as calendar, contacts , ... configured at once.
To access a delegate / shared mailbox add an IMAP account using these parameters as inspired by https://uit.stanford.edu/service/sharedemail/applemail
Whilst adding an IMAP account in Mail.app > Preferences > Accounts :
- Add Other Mail Account…:
Setup step #2:
If needed forcibly continue to next window by
alt / option click
Sign In button.
On the next windows where IMAP and SMTP server fields are showing up:
- E-mail address: email@example.com
- User Name: firstname.lastname@example.org\shared_mailbox < That's the trick to remember
- Password: yourPassword
- Fill in server settings: something like mail.domain.tld
Finish the configuration…
You may later in the first tab of this delegate account change the Email address by your own if needed…