Hi David,
There are a few pieces to this including:
- What settings are they using in their email clients?
- If they're IMAP and don't have their email downloaded you'll need the existing email & folders transferred to the new hosting company
If they have Godaddy server names in their email clients you'll need those replaced with the names for the new company, or transition them to names within their domains that will be more portable now and in the future. For example, imap.secureserver.net vs imap.their-domain.com.
You'll need to figure out what works best for existing email. Maybe that means download with POP3 and create new profiles for IMAP at the new host. Maybe that means copy to local folders. Maybe that means copy to the new service with something like the
IMAP Tools so you don't need to worry about how users are managing to save their existing email.
There will probably be more questions after you think about this some more. Don't forget to drop the TTL's in their zone files before the migration if you plan on using DNS changes to cut your users over from the old server to the new server.
Also, to manage the support load, I recommend moving them one at a time and not trying to move them all in the same night. Even with a solid plan, some mail programs might not handle the change gracefully resulting in duplicate emails or user error such as deleting an existing profile causing email to be lost.