Unfortunately you can't post links until you reach a certain number of posts as recently spammers have been registering and posting 1 post full of spam and links to unpleasant or off topic pages.
Unless you can post the e-mail here (which I can imagine would be a problem if the e-mail contains personal or sensative information) or think of the words that the spam filters might be blocking then we might hit a bit of a dead wall on the forum.
Have you opened a ticket with support (support.eukhost.com or support[at]eukhost.com) about this issue?
[edit: Sorry I didn't see the 2nd post - if eUKhost have done a test and it has worked but a certain email is getting through from and address it would imply that it is something relating to the content of the email - such as a banned word like you suggested]