I get this error returned 'sometimes' when sending email from my outlook web email to my friend's outlook web email.  I only get this sometimes though. What can be done about it? My friend is worried she is missing a bunch of emails from people if other people are getting this also.

Thanks

Error is

Reporting-MTA: dns;snt0-omc4-s17.snt0.hotmail.com
Received-From-MTA: dns;SNT148-W41
Arrival-Date: Fri, 2 Aug 2013 15:17:40 -0700

Final-Recipient: rfc822;*** Email address is removed for privacy ***
Action: failed
Status: 5.5.0
Diagnostic-Code: smtp;550-(snt0-omc4-s17.snt0.hotmail.com) [65.55.90.220]:19503 is currently not
550 permitted to relay through this server.