[Rob]

The website is being hosted on 1and1's servers.

The exchange mail server is located in my office. It's hosted on an ADSL connection with fixed IP. The mailserver itself does not have it's own domain name.

Email has been received, and sent using 4 different domains, each registered with the same host, 2 being.co.uk 2 being .com. That suggests the server is configured correctly and this the DNS / MX records being the issue.

For the mydomain.com accounts which I haven't started to migrate to the new host yet the records are:

dig any mydomain.com
;mydomaini.com. IN ANY

;; ANSWER SECTION:
mydomain.com.com. 16899 IN A 195.xx.xx.xx (webhost server IP)
mydomain.com. 16899 IN SOA ns0.awebhost.net. hostmaster.awebhost.net. 2007082401 172800 3600 1728000 172800
mydomain.com. 16899 IN MX 10 smtp.awebhost.net.
mydomain.com. 16899 IN MX 20 mail2.awebhost.net.
mydomain.com. 16899 IN MX 5 mail.mydomain.com.
mydomain.com. 16899 IN NS ns1.awebhost.net.
mydomain.com. 16899 IN NS ns0.awebhost.net.

;; AUTHORITY SECTION:
mydomain.com. 16899 IN NS ns1.awebhost.net.
mydomain.com. 16899 IN NS ns0.awebhost.net.

;; ADDITIONAL SECTION:
mail.mydomain.com. 4375 IN A 79.xxx.xxx.xxx (MY EXCHANGE SERVER IP)
ns0.awebhost.net. 64653 IN A 217.###.###.###
ns0.awebhost.net. 64653 IN AAAA 2001:***:*:****::1
ns1.awebhost.net. 64653 IN A 195.###.###.###
ns1.awebhost.net. 64653 IN AAAA 2001:***:*:****::2