When friends try to send me an email they get the following message 
Mail Delivery Subsystem <mailer-daemon@>
12:46 PM (0 minutes ago)
to me
Delivery to the following recipient failed permanently:

     *** Email address is removed for privacy *** (i have added x's in place of name ending) 

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain hotmail.com by mx1.. [65.55.33.135].

The error that the other server returned was:
550 Requested action not taken: mailbox unavailable