Can't send mail to yahoo mail addresses

i get this error

Reporting-MTA: dns; ghost.techiedistrict.com X-Postfix-Queue-ID: 601AD14343D X-Postfix-Sender: rfc822; [email protected] Arrival-Date: Sat, 17 Oct 2015 15:58:00 +0100 (WAT)

Final-Recipient: rfc822; [email protected] Action: failed Status: 5.0.0 Remote-MTA: dns; mta6.am0.yahoodns.net Diagnostic-Code: smtp; 554 Message not allowed - Headers are not RFC compliant[291]