OT Verizon rejecting emails from gmail

[Derek Trotter]

I don't know who else to ask, but yesterday and today I've had trouble 
sending email to a friend who has a verizon.net address.  Verizon keeps 
rejecting them.  Here's what I get back from them.  I just don't know 
who else to ask.  Has anyone else had this trouble?

thanks

Message-id:<4FF90584.6030107 at gmail.com>
   Date: Sat, 07 Jul 2012 20:59:00 -0700
   From: Derek<######@gmail.com>
   To: John<######@verizon.net>
   Subject: just checking

Your message cannot be delivered to the following recipients:

   Recipient address: @relay.verizon.yahoo.com:######@verizon.net
   Original address:######@verizon.net
   Reason: SMTP transmission failure has occurred
   Diagnostic code: smtp;554 Message not allowed - [320]
   Remote system: dns;mx1-vzn.mail.yahoo.com (TCP|206.46.172.79|34174|67.195.168.231|25) (mta1012.vzn.mail.ac4.yahoo.com ESMTP YSmtp service ready)