Your primary mail server is not always going to be available. Sometimes that's planned: a maintenance window, a tenant cutover. Sometimes it's not: an outage, a hardware failure, a bad DNS change pushed at the wrong moment. Without a secondary MX, senders retry for a while and give up.
Backup MX is the secondary mail server that catches inbound traffic while the primary is unreachable, queues it, and replays once recovery completes. No bounces, no lost messages.
Backup MX is the lowest-friction product in the Route group. You add a second MX record at a higher priority value than the primary, point it at us, and the mechanism is in place. The day the primary goes unreachable, senders fall through to the secondary. The day the primary comes back, the queue replays. Your team did not have to log in and flip anything.
The same product is the cutover safety net inside Tenant Migration. When DuoCircle moves an M365 or Workspace tenant, Backup MX absorbs the inbound during the propagation window between the old MX and the new one. One mechanism, two use cases. The architecture is small enough to be reliable and old enough to be boring.
Secondary MX, queue, replay on recovery, spam filtering before the queue, planned-window coverage, cutover-window coverage. Six things, all running on the SMTP backbone we have been operating since 2014.
Lower MX priority than your primary. When the primary stops accepting mail, senders fall through to the backup automatically. The backup accepts mail, queues it, and waits. You do not have to flip a switch or call anyone for the failover to happen, because the failover is just SMTP doing what SMTP has always done.
Once your primary mail server is reachable again, queued mail is replayed in order. Senders see no failure on their side; recipients see mail show up as if there had never been an outage. The replay is throttled so the primary is not flooded the moment it comes back up.
Incoming mail is filtered at the secondary before it lands in the queue, so when the primary comes back you do not get a flood of queued spam being replayed alongside real messages. The filter pass at the backup is the same one running on our spam-filtering infrastructure.
Schedule a maintenance window and Backup MX handles the inbound traffic for the duration. Patch the primary, replace hardware, fail over a database, take the time you need. There is no customer-visible outage on the inbound mail side, because mail keeps flowing through the secondary and replays when you come back.
When DuoCircle runs a Microsoft 365 or Workspace tenant migration, Backup MX absorbs the propagation window between the old MX and the new one. The same machinery that protects you from an unplanned outage protects you from a planned cutover. One mechanism, two use cases.
Backup MX runs on the same SMTP backbone that handles outbound relay, forwarding, and migration cutovers across the rest of the DuoCircle portfolio. Capacity, monitoring, and operational expertise that has been evolving since 2014, not a service stood up last quarter to fill a feature gap.
Your mail is fully cloud-hosted on Microsoft 365 or Google Workspace and you do not run any mail infrastructure of your own. The cloud platform handles its own availability and you do not have a primary mail server to back up. Backup MX shines when there is a primary you operate, not when the platform owns the whole inbound path.
You need full disaster-recovery-tier email continuity with extended outages measured in days, full inbound and outbound continuity, and an interim sending capability for a workforce. That is a different category of product. Backup MX queues inbound and replays on recovery; it does not pretend to be a continuity desktop.
You only need outbound continuity. Backup MX is an inbound mechanism. If your concern is keeping outbound application mail flowing during your own infrastructure problems, look at Outbound SMTP for the relay layer.
When you contact us about Backup MX, the person on the call is the kind of expert who has actually configured Backup MX for production environments and used it as the safety net inside tenant cutovers. We tell you the priority values to use, the queue retention, the failover behavior, and what to expect when the primary recovers.
Reference calls with existing Backup MX customers are available on request. Setup is direct rather than self-serve, because Backup MX is the kind of product where getting the MX configuration right the first time is worth a fifteen-minute conversation.
Same-day response. Real expert on the call. We tell you the configuration, the queue retention, and how it ties into the rest of your routing setup.