Do BT have the right to withhold my Emails

oldwiring

Mine has five settings but I don't know the definitions.

oldwiring

Mine has five settings but I don't know the definitions.

White listing must have some worth in unblocking mail?

Trinitrotoluene

All of this hassle and you STILL have your domain with BT?

As has been suggested - move it away. As you have quite clearly suggested that e-mail is business critical for you I suggest http://www.google.com/apps/intl/en/business/features.html

Once you have put your domain on somewhere like 123-reg you can point the mail servers at google and they will collect all your e-mail. The gmail interface and spam detection is probably the best in the world (in my opinion).