“Bulk” has started appearing in the subject line of my emals – in and out – why and how do I stop it?

Windows 7 - Windowns Live Mail -

For some unknown reason, several months ago, all my emails suddenly appear with the word "BULK" in the subject line.

I don't do it, don't know why it's there.  I think it must be another of Microsoft's not so smat add ons that I don't want

and don't need.  How can I get this to stop?

Tonight I received a email, read it, forwarded it.  Nowhere in that email did I see the world "BULK", but when the addressee

received it - the word was there in the subject line.  When she sent it back to me - the word "BULK" was in the subject line

two times - if we bounce these emails, the word is added every time, going and coming.  She does not have this with any

one else in her address list, nor do I.  It seems to be between the two of us only.  I thought it was something coming from

her computer and she always thought it was coming from mine.

HELP!!!!!