The cPanel Backup interface can download email-forwarder configuration for a domain as a partial backup.
- Open cPanel → Files → Backup.
- Find the Forwarders section.
- Select the domain whose forwarder configuration you want to download.
- Save the downloaded file with your other account backups.
This backs up forwarding configuration, not the contents of every mailbox. Mail data is stored separately under the account's home-directory data.