When you say you send the letter, you could be using one of several methods. I suggest sending the document as an attachment, which should solve your problem.

When sending I mean I use the 'Send to mail recipient' button. This is the only real option for me because I am sending to a list of people but some are not able to receive attachments for various reasons.

It seems to me that in a so-called integrated Office suite, sending a word document by email via the most obvious method should be able to cope with sending the header and footer too....... just wish I knew how?

I have just tried sending a document the way you do, as well as by right clicking the closed document and using the send/mail recipient. Both work fine. I don;t know what could be causing your problem, and will have to leave it to someone else. Sorry I couldn't help.