Office 365 (Outlook 2013 / 2016 / 2019 for Win) - Sending E-mail From a Shared Account From Within Your Inbox (and Vice Versa)
Create a new email message.
Click on the Option tab along the top of the new message window.
Click on the From button in the email header.
Choose “Other E-mail Address”.
This will display a new pop-up window entitled “Send From Other E-mail Address”. You can either start typing the name of the address you want the message to be sent from or you can select the From… button in the window to search the address book. When you have the address you want to send from, click the OK button.
Compose your email and click the Send button when you are finished.
Anytime you create a new message from this point forward, the From box will appear. You will simply need to click the From button and select the address from the list you’ve already used or add a new one.
When sending from a shared mailbox, the sent item is placed in your Sent Items folder. There is a configuration setting on the server to have it place a copy in both your sent items folder and the sent items folder of the account you're sending from. This option needs to be requested through Campus Technologies.