Hi everyone,
I’m planning to set up a high-availability email system using two separate Mailcow instances, each hosted on different sites with different public IPs. The main goal is to ensure mail continuity during updates or outages on one of the servers.
Here’s what I’d like to achieve:
Two independent Mailcow servers (Server A and Server B), each on a different site and with different outgoing IPs.
When Server A is under maintenance or goes down, Server B automatically takes over mail reception and sending, and vice versa.
Each server should be able to handle mail for the same domain(s) without conflicts or duplicate deliveries.
Ideally, both servers should keep mailboxes and configurations synchronized, or at least queue and relay mail properly without user impact.
I’ve looked through the Mailcow documentation and forums but haven’t found a clear guide on how to achieve this. Some challenges I foresee:
DNS/MX configuration for failover.
SMTP routing and avoiding mail loops.
Synchronizing mailbox data, especially if users connect to both servers.
TLS certificates and DKIM alignment across both servers.
Potential risks of using active-active vs active-passive setups.
Has anyone implemented something similar? Any best practices, warnings, or recommendations would be greatly appreciated. I’m also open to third-party tools or hybrid approaches (e.g., using an external MTA or load balancer).
Thanks in advance for your help!
Best regards,
Mael