Exchange TXT MX SPF Records

Thank you for the clarification ...

From your description, it seems like that (although, again, I can't be completely sure) I mostly understood what you were doing with the DNS resource records ... the only thing that I didn't understand was that for every A record that you migrated, you were using a wide-IP to represent it on your GTM; not RoadRunner. (Which, of course, would allow you to take full advantage of the intelligent DNS high availability load balancing with health check / service check / content check monitors that F5 offers over the local BIND instance utilized by RoadRunner.)

However, for the MX records and TXT records -- unless they are being utilized for the hostnames under the subdomain that your ISP has granted you (MABDROSOL.ISP.COM in the example that I contrived) -- still have the same problem as in my example: a domain (or subdomain) cannot delegate its own name to other DNS nameservers. (Additionally, note that TXT records cannot be represented by a wide-IP.)

SUGGESTION: Assuming you are doing your DNS work on the public Internet, could you share one of the successful A record migrations; and one of the MX records that you are unable to successfully migrate? This would clearly allow better understanding by all of what the issues are, and facilitate recommendations on how to correct.