It's unclear what you mean by "domain names that I am going to move to a different hosting company". It sounds like you might mean "web site hosting", or you might mean "DNS hosting", or you might even mean "email hosting" (since you're using the POP3 connector for Exchange). It sounds like you might not have a handle on what all the components of your hosting service are, and if you don't know that you're likely to create some type of outage.
DNS hosting provides the translation of IP addresses in your domains to IP addresses. Looking at both of these domains, I see the following:
- DNS servers:
- MX record refers to: mail.nfsh.org.uk (aka scott.vs.man.wessexnetworks.com), a Postfix MTA
- DNS Servers:
- MX record refers to: mail.thehealingtrust.org.uk (aka 62-249-244-216.static.enta.net), a Microsoft Exchange Server MTA
Here's my guess as to what's going on: You're going to move DNS and web hosting services for both of those domains to a new hosting company.
You probably had the "nfsh.org.uk" domain first, and years ago established POP3 email accounts with that hosting provider. Later you added your SBS server, and your IT provider configured the SBS POP3 connector to go and fetch email from the mail server at "mail.nfsh.org.uk" and put it into the mailboxes for the Exchange users who had old addresses at that domian. (So, basically, email for those "@nfsh.org.uk" addresses is being sent to an email server at "wessexnetworks.com" and being held there until your SBS server computer goes and retrieves the mail with the POP3 protocol.)
You've added the "thehealingtrust.org.uk" domain later, and your IT provider configured the MX record for that domain to send inbound email directly to your Microsoft Exchange Server computer (hosted in your office and connected to the ISP "Entanet International", I'm guessing).
Assuming I'm right about these things and assuming that all email addresses for addresses "@nfsh.org.uk" need to come to your Microsoft Exchange Server computer here's what I'd do:
Make sure the new hosting company maintains all the "A" and "MX" records associated with email delivery in the "thehealingtrust.org.uk" domain exactly as-is in the new DNS. Likewise, they should maintain the "nfshdc.thehealingtrust.org.uk" record's address as-is.
Have the new web hosting company maintain the "A" record for "mail.nfsh.org.uk" exactly as-is in the new DNS. This will allow your POP3 connector to continue downloading any mail that gets delivered to the "wessexnetworks.com" mail server during your transition.
Have the web hosting company change the "MX" record for "mail.nfsh.org.uk" to refer to "thehealingtrust.org.uk" such that email for "@nfsh.org.uk" addresses henceforth will be sent directly to your Microsoft Exchange Server computer.
Have your IT provider configure the "nfsh.org.uk" domain as a valid recipient domain in Microsoft Exchange on your SBS server computer (and see that the appropriate users have "@nfsh.org.uk" addresses assigned).
A few days after the change is done, have your IT provider verify that no new mail is being delivered to the old POP3 mailboxes and disable the POP3 connector.
That should get you what you want.
Microsoft has an article here describing in broad strokes how to add an accepted domain to Exchange 2003. When they say "Open the properties of the appropriate policy..." they're saying, in your case, the "Default Policy".
A change to the "Default Policy" will cause every user to receive an "@nfsh.org.uk" email address. If that's not what you want then I'd recommend reading up on creating addt'l recipient policies to assign email addresses to subsets of users. There's a a nice starter article here that you can use as a guide.
Assuming you leave the DNS records for the "nfsh.org.uk" domain alone, email to that domain will continue to function as it always has, irrespective of changes you make to the "thehealingtrust.org.uk" DNS records.