Mailboxes & Default mailbox

[#1]

Help please: yesterday and on line +net helper said that I couldn't collect mail addressed ***@atbs1.co.uk as this domain name is no longer hosted at Plusnet = OK I accept that.  What I therefore currently have are a number of mailboxes ****@atbs1.plus.com which I want to rename/delete and replace with ****@atbs1.com (a domain that is hosted by Plusnet;  so is this possible please?

[#2]

atbs1.com is not hosted with us either.
It's registered  with enom:

Registrar WHOIS Server: whois.enom.com
Registrar URL: www.enom.com

And hosted by UK2.net:

Name Server: ULTRA103.UK2.NET
Name Server: ULTRA104.UK2.NET

In order for us to look after email for the domain, you would need to transfer the hosting to us.