We are left wondering what the solution was. As the essence of the Forum is that knowledge is shared for others to search for afterwards would either or both of you care to expand on the rather enigmatic end to this thread. And the community did provide some input too. What was wrong, what solved it - please.
As a Very Insightful Person, I'm here to share my knowledge. I don't work for Virgin Media.
Sorry I didn't post this earlier as I appreciate how important it is to share any fixes with the community.
I flagged the issue to our internet security team, our internet security team analysed the information and found the domain http://kdcs.org/contact/ was tripping our spam filter. they reviewed this domain and found it was fine.
They requested it to be de-listed. Once de-listing was completed, Linny40 was able to send the email without further issues.
I am sorry I dont any further information on why it flagged in the first place.