Windows - Sending Mail From Outlook Shared Mailboxes
If you have access to a shared mailbox and want to send email from that mailbox rather than your individual account, you will need to choose which account to send from.
Instructions
Once you have been given access to a shared mailbox you will see it listed in your inboxes on the left of Outlook
Open a new email and click the Options tab and click From
You will see a new option above the To button called From , click this dropdown and choose the relevant mailbox you want to send from
Draft and send you email as normal and once sent it will appear in the Sent Items folder for the shared mailbox you sent it from
You must have been already granted access to a mailbox to send from it. Raise an IT request if you require access.