My manager asked me to backup our Microsoft 365 mailboxes. Does Microsoft already do it for us? What are the options?

Microsoft keeps the service running and protects against hardware failure, but it is not a backup in the sense of "restore my mailbox to last Tuesday". Deleted items go to Recoverable Items for 14 days by default (up to 30 if an admin sets it), and a deleted user is kept for 30 days.

Options:
1. Retention policies and litigation hold. These keep copies of mail, but they are meant for compliance, not for restoring an inbox.
2. Export to PST. A user can export from classic Outlook, and admins can use the eDiscovery export in the Microsoft Purview portal.
3. Third party backup services that copy the mailbox to separate storage. These give you point in time restore.

Choose by how fast you need to restore and how much you need to keep. For a handful of mailboxes, PST exports on a schedule can be enough.

Very useful. We will start with eDiscovery exports and look at a service later. Thanks.