Hello mailcow community,
I would like to ask for advice regarding my sender-dependent transport configuration in mailcow.
Currently, I am running two Proxmox Mail Gateway (PMG) nodes in a cluster, which I want to use as outbound relays for mailcow.
In mailcow → Sender-dependent transports, I configured a transport with the following host value:
10.0.0.2:26, 10.0.0.3:26
This transport is active and assigned to the domain.
However, I noticed that in the domain configuration, only one sender-dependent transport can be selected per domain, so I cannot assign separate transports per PMG node.
When testing the transport, I receive the following error:
- No MX records for
10.0.0.2:26,10.0.0.3:26 were found in DNS, skipping and using hostname as next-hop
- Invalid host:
10.0.0.2:26,10.0.0.3:26
- SMTP connect() failed
My questions are:
- Is it supported to define multiple relay hosts in a single sender-dependent transport (comma-separated) in mailcow/Postfix?
- Since only one sender-dependent transport can be assigned per domain, what is the recommended way to use a PMG cluster as outbound relays?
- Should I:
- Use a virtual IP (VIP) or load balancer in front of the PMG cluster?
- Configure DNS (e.g. a hostname resolving to multiple PMG IPs)?
- Or is there a specific Postfix transport syntax that mailcow expects in this case?
I want to ensure this setup is correct and follows best practices for mailcow + Proxmox Mail Gateway.
Thank you in advance for your help.
