Mail server with multiple domain IP addresses

By telemark39 ·
Hi, just joined this interesting forum.

Been trying to find a solution for the last couple of weeks!
Currently our mail server is at an external site. It has all our company mail domains pointing to that external mail server address.

We would like to install our own company Mail Server (not exchange) locally. we would like to have all our mail domains pointing to their own public IP addresses. How would the mail domains find thrir way to the server. We have a firewall which I manage. Thanks

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DNS MX Records

by Churdoo In reply to Mail server with multiple ...

The public DNS for your company domains is what directs things to services such as email, website, etc.

Find where the DNS for your company domains is hosted, probably at the same site as the external mail servers, and inspect the MX records for your domains. You'll see that this is what directs email to the external mail servers.

When the time comes to switch mail delivery to your internal server(s), you will change the MX and/or corresponding A records accordingly.

Note that this is not necessarily an immediate effect -- due to DNS caching, it may take 24-48 hours and sometimes longer before sending mail servers recognize this change, so generally such changes are made at the beginning of a weekend so that propogation is complete by the beginning of the next work week.

Also note that it is possible to have multiple MX records and different preferences, thereby allowing redundant mail servers and/or backup mail servers.

Hope this is what you were looking for.

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Multiple MX records

by telemark39 In reply to DNS MX Records

Thanks churdoo, that make so much more sense now. much appreciated.

We'll then allocate each domain a public IP address and update the MX records. This way we can migrate one at a time!

All I have to do now is to work out how the new local mail server is going to be set up with regards to IP addressing. Do I use a local IP address for each domain then NAT from the router to the relevant local IP on the server?

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static NAT

by Churdoo In reply to Multiple MX records

Yes you can use static NAT's.

Keep in mind, you don't necessarily have to dedicate one IP address per domain. You can have a single IP address service multiple domains. That part is up to your preference.

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Multiple domains

by telemark39 In reply to static NAT

Inrteresting. Reason multiple addresses is required to keep them separate rather than show the same IP address for all.

Seems so close to a solution. We have a block of 6 public addresses something like (So if the router public address is say, can we then use this for the primary mail domain and then use to for the other four mail domains, but somehow redirect them to the 1.1 IP address. That way they would have their own IP addresses, but all hit 1.1. Then NAT 1.1 to the local server IP address. Will this work or is there a better way? I'm trying to make it simpler also at the LAN end. Thanks

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Simpler than that

by Churdoo In reply to Multiple domains

Multiple IP's are not required from a DNS or delivery standpoint. Only if your internal mail server configuration requires multiple IP's will you need multiple IP's. And the only reason I can think that that may be required, would be for sending email, for example if you configure multiple virtual servers wanting each to have its own identity, but even that's not required.

As an example, you can prep your mail server for the email processing and NAT to your mail server internal IP.

To switch the email for the first email domain, add a DNS A record for -> and change that domain's MX record for mail delivery to

When ready to switch the next email domain, then just switch its MX record to deliver to Yes it's legal for the MX record of to point to the server, but if you feel more comfortable, you can create -> and point MX to that.

and so on.

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