Mailcow Dual Server Setup Request for Guidance

Selvamohan

Hello Team, this is Selvamohan.
I hope you’re all doing well.
I’m currently in the process of setting up a Mailcow email infrastructure.
Plan Overview
I’m planning to set up two Mailcow servers:
The primary mail server will handle regular user email traffic (sending and receiving).
The secondary mail server will be dedicated to sending automated emails, such as system-generated notifications, transactional messages, or bulk emails, without requiring SMTP authentication. The goal of this setup is to isolate automated email traffic from the main server.
Mail Server Domains
mail.domain.com – Primary Mail Server
smtp.domain.com – Secondary Mail Server
The primary Mailcow server has already been successfully set up and is functioning correctly. The secondary server setup is almost complete, but I need help with configuring the IP that will be used for sending automated emails. If you have any steps or suggestions on how to configure this.
Additional Query
Is it possible to configure DKIM records for both subdomains (mail.domain.com and smtp.domain.com) since they are based on the same main domain?
Kindly assist me with the above queries.

esackbauer

You need to have at least 2 public IPs available at your host. Even better is using 2 different hosts.
Otherwise if using one host, install mailcow in 2 different directories and use 2 different compose project names during initial configuration.
DKIM is valid for a mail domain, not a “subdomain” which is actually a FQDN.

Selvamohan

Hello Mr esackbauer

Thank you for your message.

You need to have at least 2 public IPs available at your host. Even better is using 2 different hosts.
Yes, I’m using two static public IP addresses and two separate Mailcow servers.

For example, the domains are structured as follows:
mail.domain.com – Primary Mail Server
smtp.domain.com – Secondary Mail Server
Here, domain.com is the main domain. Based on this, I’ve created both mail subdomains and added the necessary SPF and DKIM records.
For SPF, I’ve included both server IPs in a single record under the main domain.
For DKIM, I’ve only set it up based on the primary mail domain (mail.domain.com), so currently DKIM is working only for that.
However, DKIM is not working for the secondary domain (smtp.domain.com). Is it possible to generate a separate DKIM record for the secondary Mailcow server under the same main domain? If so, could you please guide me on how to achieve this?

Looking forward to your feedback.

esackbauer

Just use a different DKIM selector.

Selvamohan

Mr. esackbauer

Thank you. I have added the DKIM record, and it’s working well.

And can you share any suggestions for my remaining queries?