[BlueOnyx:03100] Sendmail

[Andrew P]

I installed a new site that was using the standard PHP mail option, however I was getting the 
following errors with certain email addresses;

----- The following addresses had permanent fatal errors -----
<pincotta at tpg.com.au>
    (reason: 553 5.1.8 <pincotta at tpg.com.au>... Domain of sender address
apache@*****.com.au does not exist)

I noticed in the website admin console that it had the option to use the built in sendmail, I changed 
the drop down to sendmail and entered "/usr/sbin/sendmail" as the sendmail path. I dont get an 
error message when attempting to send mail however the mail never arrives.

Is there anything I have to do to use the sendmail option?

Thanks.