I suspect you may be confusing making intermediate changes to the DNS
zone files on Gradwell with transferring registrars. I have moved over
half a dozen domains from Gradwell to Tsohost; both pre and post
Gradwell's 'migration' to their cloud legacy hosting management
panels. I don't these days have any other users to worry about but I
am still my own user (multiple domains and two mail clients).
1. You don't have to make any DNS changes at Gradwell in advance of
setting up web and mail hosting configurations on Tsohost.
2. Before the control panel changes at Gradwell (from Developer
account panels to the cloud legacy hosting panels) moves took place in
the following staggered fashion:
2.1 Create a new 'temporary' zone file for the domain being moved:
2.2 Change MX record to point to Tsohost mail servers. AFAIR users are
still able to access their Gradwell mail boxes at this point, all
that's changed is that incoming mail will be sent (progressively as MX
field change propagates) to Tsohost's gridhost servers. In addition
the new Tsohost mailboxes can also accessed as they are gridhost and
not bespoke domain addressed.
2.3 When 2.2 complete change A records so web site is delivered from
Tsohost.
2.4 When 2.3 complete change NS records to point to Tsohost
nameservers.
3. At this point subject to zone file changes propagation, all dns
requests will be directed to Tsohost.
4. Finally, transfer registrar's by whatever process suits you best.
Before the control panel changes I used to make the Tsohost account
panel change notifying Tsohost of the incoming transfer, change the
Tag in the Gradwell panels and raise a ticket to Gradwell to 'release
the domain'. More recently, partly because I couldn't locate where to
change the Tag on the new Gradwell panels and partly because Gradwell
were ignoring tickets raised for them to do it, I did it myself by
opening an account with Nominet.
5. Another difference since Gradwell implemented the new Cloud legacy
hosting panels is that I went straight to 2.4 as I had problems
changing the other records (MX, A etc) in the new Gradwell panels.
This may have been down to a mental block on my part, i.e. maybe I
gave up to soon.
Chris S