Do Shared Mailboxes Require Microsoft Defender for Office 365 Licensing?

If you’re planning to access the shared mailbox and use features like Safe Attachments or Safe Links, you definitely need a separate license for it. Just having the users licensed won’t cover it if those features are applied.

Shared mailboxes won't require a license unless you're exceeding the 50GB storage limit. But your concern seems to be about protection; that’s where you'd need the defender license.

I get what you’re saying about the potential protection. It’s a valid question since there’s confusion regarding whether the MDO license extends to shared mailboxes or not.

For a shared mailbox to benefit from Defender, all users accessing it need to have their own Microsoft Defender for Office 365 licenses. So, yes, that shared mailbox does require licensing. It’s a bit tricky, but if you want to unlock advanced features, it must be licensed too.

Actually, shared mailboxes don't typically need a license unless you're logging in directly as that mailbox to send emails. If the mailbox is just for receiving, you can have licensed users send as it without assigning a license to the mailbox itself.