What Backup MX Does
Backup MX is a secondary mail server safety net. It sits behind your existing primary mail server at a lower MX priority. If your primary goes down — planned outage, hardware failure, maintenance window — senders automatically fall through to the backup, mail queues, and when the primary comes back online the queue replays automatically. It is designed for organizations that run their own mail infrastructure and need a failover net behind it.
What Tenant Migration Does
Tenant Migration is a dedicated email queuing service built specifically for tenant-to-tenant migrations on Microsoft 365 or Google Workspace. You temporarily make it your only MX record. It holds all inbound mail — up to 45 days — and releases it only when you manually trigger delivery through the portal, once your new tenant is fully configured and ready to receive mail.
Why This Matters for Your Migration
The critical difference is what controls the release of queued mail.
Backup MX releases automatically the moment it detects the destination server is responding. During an M365 tenant migration, your new tenant will respond on port 25 before it is fully ready to receive mail. Backup MX would interpret that as a recovery and begin delivering — into a tenant that isn't configured yet. That is exactly the failure mode you are trying to avoid.
Tenant Migration holds mail regardless of whether any server is responding. Nothing is delivered until you configure it to release. That deliberate, manual control is what makes it safe during a cutover window.
What to Use for a Tenant-to-Tenant Migration
For a tenant-to-tenant M365 or Google Workspace migration, you need Tenant Migration. It was built for this specific use case and gives you full control over when mail is released to the new tenant. Backup MX is not the right tool for a migration scenario and would not protect you correctly during the cutover window.
If after your migration is complete you want ongoing secondary MX protection for your domains, Backup MX is worth considering at that point — but that is a separate decision for after the migration is done.