MIAB as Backup Relay Server?

I’m running two MIAB virtual machines for two separate domains on a TrueNAS server. I’m using GODaddy DNS and have entered all the recommended entries on the MIAB External DNS screen for each domain. One domain is live and receiving email. The other is in progress.

Is it possible, or necessary, to setup a separate MIAB server on another machine to act as a Backup/Relay to catch and forward messages if the primary servers are down?

I searched, but there isn’t anything recent on the topic.


From the post @eXTric linked…

However, they can only retry mail if there is a DNS record. The way MiaB is set up, you must take extra steps to set up Secondary DNS.

Either this, or you can do DNS entirely via an external provider, e.g. via your registrar. See Advanced Usage with External DNS

On the other hand, I am not sure if e-mails are really getting lost, just because the mail server and DNS are down at the same time. I mean the sending mail server tries to resend the mail several times, and when Mail-in-a-Box is up and running again, so is DNS.

Nevertheless it certainly makes sense to have at least one secondary DNS server. Especially if your Mail-in-a-Box also manages DNS records for services hat are running on other servers. Otherwise, If Mail-in-a-Box is down, the records for all these sites can no longer be resolved too.

Hi. Having a second mail server really depends on your use - for a major corporate, yes, but they are probably duplicating lots of infrastructure, and that’s not really what MIAB is aimed at.

Email is “store and forward”. As long as a server can see that your domain exists (you should have a main and a secondary DNS server), it will save emails for quite some time, until your email server can accept them.

For your own couple of domains, with a few users, I’d say don’t bother with a second mail server. But be sure to have a second DNS server. I don’t know about GoDaddy but many DNS providers have a free backup DNS service. You just point that at your server and it maintains a duplicate of your DNS.

I appreciate the response. When I started running my own email (over 15 years ago), it was two separate Windows Servers for email and two Red Hat boxes for DNS. With the last ISP change, I started using GoDaddy to host my DNS so that it’s always available and I don’t have to maintain the servers. I’ve just finished migrating the email from two Windows 2012 Servers to two MIAB VM’s under TrueNAS on a Dell Server. I just wasn’t sure if it was necessary to try and run a backup to store and forward email if the servers are down.

Let me expand upon this just a little. Keep in mind that when you are hosting DNS on your MiaB and DO NOT have Secondary DNS somewhere that when MiaB is down, your DNS is also down.

Now when someone attempts to send email their server does a DNS lookup for your domain’s MX record. If that record is not found the mail fails permanently.
However, if there is a secondary DNS the MX record lookup will complete and their mail server will try to send your mail.
If they cannot connect to your server, they will re-queue the email for later delivery. Then most mail servers retry 2mins, 4mins, 8mins, 16mins, 32mins, 64mins, 128mins, 256mins, 512mins … and so on, later until either they can deliver the email, or give up after 2-5 days (dependent upon the settings chosen by that providers admin).

No, not really in this day and age. See my previous post in this topic which explains the logic.