How to stop multiple copies of an e-mail?

31. May 2012 · Write a comment · Categories: Hotmail · Tags: , , , , ,
Over the past couple of years I have been sending out a newsletter to a group of friends.   
On my last mailing, a friend in USA complains that he has received over 60 copies of the e-mail although it was only sent once. None of my settings have been changed.
He is the only person with this problem & the only person in USA that I send to, although I also send to countries including Canada, South Africa, Asia & Europe.   Any ideas how these e-mails can be stopped?  
Mike