Hi
It is best to make contact independent from email if your ever not sure.
However that said, it appears to be genuine from the little information you posted
If a domain is TAG changed to a new provider but the new provider is not aware of the incoming domain, it is placed into a holding account until either the owner claims it by notifying the provider of the domain or domain expires
The above happens simply because the new provider does not know which account to put the domain into....
Also, until the domain has been claimed, all dns is set by the provider and no changes could be made by the owner until claimed
An easy way to determine if email is genuine would be to a simple Whois lookup and that will tell you if 123reg or dyno - so if 123reg - email not genuine but if dyno email is likely to be genuine
Many thanks
John