Backing up an Office 365 mailbox manually can become difficult when the account contains years of emails, attachments, contacts, calendars, and other mailbox items. For a proper backup, I would first decide whether I need the complete mailbox or only selected folders and date ranges.

One approach is to use a dedicated Office 365 backup tool that can access the mailbox and save the data locally. SysInfo Office 365 Backup Tool supports saving mailbox data in formats such as PST, PDF, EML, MSG, MBOX, and CSV. It can also work with primary mailboxes, online archives, shared mailboxes, and public folders.

The useful part is that the backup does not have to include everything. The software provides folder selection and date filtering, so users can choose the required mailbox content before starting the backup. It also supports saving emails with or without attachments and provides an option to skip previously migrated items.

For larger environments, batch processing can be useful because multiple Office 365 accounts can be handled in the same backup workflow. Modern Authentication is supported for accessing Office 365 accounts, which is important when working with current Microsoft 365 environments.

My usual approach would be to preview the mailbox first, select the required folders, apply a date filter if necessary, choose PST or another suitable output format, and save the backup to a separate local location. This keeps the backup process more organised and avoids manually exporting individual emails one by one.