Ah..... I'm glad I'm not the only one having the same problem, I too cannot send to a particular hotmail recipient for the last couple of weeks.
I Have sent loads of emails to her, but none have arrived and like you, I'm with orange and thought because my email address has freeserve in it, hotmail has been blocking them.
I use Thunderbird as my email client with no luck, I then sent her an email via my Orange web mail with no luck. I suggested she sent me an email so I could REPLY to it, so as to avoid typo errors...still no luck!
This is most frustrating as I can receive all her emails with no problem.
I live in hope...........thanks SURVEY.