5.7.1 smtp; 550 5.7.1 relaying denied

[rejohn]

I'm getting the following error message while recieving mail from apa.org domain. This seems to be a relaying issue with my smtp servers, how can I correct this ?

Reporting-MTA: dns; APAEMAIL-4.apa.org

Final-Recipient: RFC822; robert.e.johnson@usm.edu
Action: failed
Status: 5.7.1
X-Supplementary-Info: <APAEMAIL-6.apa.org #5.7.1 smtp;550 5.7.1 <robert.e.johnson@usm.edu>... Relaying denied>
X-Display-Name: robert.e.johnson@usm.edu

Final-Recipient: RFC822; Celso.Lima@usm.edu
Action: failed
Status: 5.7.1
X-Supplementary-Info: <APAEMAIL-6.apa.org #5.7.1 smtp;550 5.7.1 <Celso.Lima@usm.edu>... Relaying denied>
X-Display-Name: Celso.Lima@usm.edu