OST to PST conversion in Outlook 2021 is an effective way to secure and transfer mailbox data. OST files are designed for offline access and are dependent on Outlook profiles. Using conversion software, users can convert mailbox contents into PST format for long-term storage and easy accessibility. The software supports emails, contacts, calendars, tasks, notes, and attachments. It also maintains folder hierarchy and email properties. This process is highly beneficial for backups, migrations, and disaster recovery situations.