Hi,
The best thing you can do is to ask him the following:
- How many (POP/IMAP) accounts do you have at the old webhost?
--> Did he check the accounts through a webmail client or a computer based client (like Outlook?)
- Are there any redirects setup
- Is there any special wishes entered in the MX record of the domain at the old domain provider?
In case all go wrong I advice you to keep the domain at your preffered supplier (123-reg) but point the DNS records back to the
old webhost. Everything will be as it was. And you can take your time doing this important part of a domain transfer.
Goodluck,
Faisj