Email can send but not receive

Email can send but not receive

I am having difficulty receiving email.  I have checked my MX records and they are correct  I get this error:

Reporting-MTA: dns; googlemail.com
Received-From-MTA: dns; tristanwthomas@gmail.com
Arrival-Date: Fri, 03 Feb 2017 07:38:37 -0800 (PST)

Final-Recipient: rfc822; tristan@tristom.com
Action: failed
Status: 5.0.0
Remote-MTA: dns; mail.tristom.com. (50.116.114.151, the server for the domain tristom.com.)
Diagnostic-Code: smtp; 550-Please turn on SMTP Authentication in your mail client, or login to the
 550-IMAP/POP3 server before sending your message.  mail-qt0-f193.google.com
 550-[209.85.216.193]:34708 is not permitted to relay through this server
 550 without authentication.
Last-Attempt-Date: Fri, 03 Feb 2017 07:38:47 -0800 (PST)

What is the problem? Please advise