Hello BenjaminMontré,
Firstly, If someone suggested you contact the support via phone number, it is a spam and please ignore the spam or report it. We are monitoring our forum to avoid the spam. And we will have actions for these replies immediately once we notice them.
Based on my researches and tests, there is no such PowerShell to add From field automatically. Given this situation, I will share the detailed steps to add From field in Outlook client and Outlook Web App with you.
In Outlook client:
1. Click New Email to compose a new email.
2. Click Option tab and selectFrom in Show Fields group.
3. Then click From > From and choose the shared mailbox in the global address book to send emails.
In Outlook Web App,
1. Click the gear icon at
the upper-right corner of the page.
2. Then click View all Outlook settings at the bottom.
3. Select Mail > Compose and reply, then find Message formatand check the option Always show From, then save the changes.
Outlook will remember the mailbox once the user sent an email from the shared mailbox, so the users can directly click the drop-down button besides From and choose the shared mailbox in the drop-down list.
Hope it can help you.
Regards,
Seven