strange email-receipt

i received two identical mails within one day from an unknown person but in both of them the “to:”-adress was not mine but from a third unknow person. i have found this hotmail.com-adress in a guestbook of an other photographer(i am photographer). i have a hotmail.com-adress but this one was not affected. i even do not have an entry in the guestbook, not in that section but in another.
are my coming-in-messages being watched of hacked?