I understand how MX works in that I can either load balance using equal priorities or I can have smarthosts using high low priorities. I get this.

Like many, I host many domains so have one domain (mydomain.com) which has an MX and reverse record pointing to the mail server (let's call it mta.mydomain.com) which hosts email for multiple domains.

In this case, there is an upstream provider which handles it's own DNS which means I need to contact them to have reverse records created, even though I run my own DNS servers beyond that. I cannot contact them and ask them to create a reverse every time I host a new domain because they will mess that up. Hence, I have one mta.mydomain.com record and a backup which I do use as a smarthost only.

Now I need to test a new mail server but it needs to be on the mydomain.com as well so I've set it up as mta2.mydomain.com.

I've taken a few domains off of the mta.mydomain.com mail server and put them on the mta2.mydomain.com mail server.

Of course, email coming in is now trying to get on either server, depending on which responds first so of course, sometimes fails.

So the question is, how do I test the new mail server which is in the same domain but not have balance or backup routing issues. I suspect that I only need to remove the mta2.mydomain.com MX record from mydomain.com and only put it into the domain records which I've moved to the new server? I didn't want to try this yet because I don't want to create any propagation problems.

And, I certainly hope I've explained this correctly and am happy to further explain if not.

Thank you kindly.

Yes , In absense of MX record A record pointing to an address can work as MTA.


Thanks

Split domain routing is useful for things like migrating mail domains from one server to another. You may want to look into setting it up for your particular MTA. It will basically take any email accounts within a specified domain not present on mta.mydomain.com and forward them to mta2.mydomain.com.

What I dont get is why the remote ISP needs your ptr records? Are the responsible for this ptr's?
Maybe spf might help out with this particular ISP.

Thanks for all the input, this works as it should now.
My mistake was to put both mail servers in the master MX record which was causing the mail to behave as if being smart hosted. My need was to in fact flow email to different servers.

As for why this is needed upstream, it is because unlike our dedicated circuits where we control the entire IP range for DNS, sometimes, the provider is a cable company which doesn't seem to really understand 'business' needs. Maybe in time they will but right now, it's a pain because unless I have them mod their records, email bounces because the return reverse is their IP.