Lots of mails from apache

[RA]

Hello,   I'm running RH 7.1 and have configured mail, web, squid servers on it. all services are working good, but apache sends lot of messages to xyz@aol.com, where xyz is random value, and all the mails come back to me. I would like to know why, and how apache sends these messages, and if there is a way to deny apache to send mails ?   Thanks in advance.