Setting up backup MX records involves a few steps:
Identify a reliable secondary mail server. This could be another server you control or a third-party service. Access your domain's DNS settings through your DNS provider. Add a new MX record with a higher priority number than your primary server. Lower numbers indicate higher priority, so your backup server should have a higher number. Test the configuration to ensure that emails are correctly routed to the backup server when the primary server is unavailable.