Can send, but not receive email

Can send, but not receive email

This is the error message I keep getting when trying to test sending an email to my Zoho email:

 Message-id: < 95BD621F-6688-4B77-8634-FAAFB065128C@icloud.com >
 Date: Fri, 11 Apr 2014 19:05:16 -0400
 From: Benjamin Henson <ben.henson@icloud.com>
 To: planhenson <ben.henson@planhippo.com>
 Subject: Still?

Your message cannot be delivered to the following recipients:

 Recipient address: ben.henson@planhippo.com
 Reason: Remote SMTP server has rejected address
 Diagnostic code: smtp;550-Please turn on SMTP Authentication in your mail client, or login to the IMAP/POP3 server before sending your message. st11p02mm-asmtpout001.mac.com(st11p02mm-asmtp001.mac.com) [17.172.220.236]:37145 is not p
 Remote system: dns;planhippo.com (TCP|17.172.220.236|37145|192.185.39.240|25) (gator4096.hostgator.com ESMTP Exim 4.80.1 #2 Fri, 11 Apr 2014 18:05:34 -0500 )

Original-envelope-id: 0N3W00F8X2STD230@st11p02mm-asmtp001.mac.com
Reporting-MTA: dns;st11p02mm-asmtp001.mac.com (tcp-daemon)
Arrival-date: Fri, 11 Apr 2014 23:05:17 +0000 (GMT)

Original-recipient: rfc822;ben.henson@planhippo.com
Final-recipient: rfc822;ben.henson@planhippo.com
Action: failed
Status: 5.0.0 (Remote SMTP server has rejected address)
Remote-MTA: dns;planhippo.com (TCP|17.172.220.236|37145|192.185.39.240|25)
(gator4096.hostgator.com ESMTP Exim 4.80.1 #2 Fri, 11 Apr 2014 18:05:34 -0500 )
Diagnostic-code: smtp;550-Please turn on SMTP Authentication in your mail
client, or login to the IMAP/POP3 server before sending your message.
st11p02mm-asmtpout001.mac.com (st11p02mm-asmtp001.mac.com)
[17.172.220.236]:37145 is not p