Server 1 -> mail.myhomeserver.com
-> Current website domains/email on this system working perfectly:
- mydomain.com (my main email account on this domain)
- yourdomain.com
- herdomain.com
- hisdomain.com
- theirdomain.com

Server 2 -> mailsvr.mydomain.com

I currently have Server 1 setup in my house as a mailserver. I've decided to move it out of my house as this was a really bad idea for performance reasons.

I want to setup the new server, migrate the accounts over one at a time and make sure they are working (by setting the MX records one domain at a time).

I have created a new A record: mailsvr.mydomain.com which resolves to my new mailserver IP address.

I have NOT changed my MX records for mydomain.com yet because I want to test one of my non-used email accounts first (lets say domain herdomain.com). So my goal is to migrate the email boxes on herdomain.com over to the new server. Then setup the new MX record at herdomain.com to point to mailsvr.mydomain.com and hopefully it should start working.

I'm currently setting up BIND on mailsvr.mydomain.com. If I create an MX record on this BIND server but don't change the MX record in mydomain.com right now, will it mess up my current setup?

I hope this hasn't been too confusing but it is hard to type it out in a clarifying way.

I should probably mentioned that the DNS management is handled on a different server:

So my DNS flows like this:

Domain Registrar > Hosting Server > mail.myhomeserver.com

All the A records pointing to mail.myhomeserver.com are defined on Hosting Server.