If you need to save an Office 365 mailbox as a PST file, Outlook’s built-in export option may work for a smaller mailbox, provided the required data has synced properly. For larger mailboxes or multiple accounts, a dedicated backup tool can be more convenient.
You can consider BitRecover Office 365 Backup Tool to export Office 365 mailbox data to PST. Before starting, check that the tool supports the mailbox type you need to back up and review its available folder-selection options.
