[CentOS] root at localhost email problem

I have another problem with the email root at localhost not working now on
centos 3.5 with plesk.

This has always worked in the past.  Anytime I test my ecommerce store the
default email address has been root at localhost and has sent an email to my
domain email address when testing.  Just recently this has stopped working.
The ecommerce store is php.  I contacted the ecommerce store developer and
root at localhost works for him and he is hosting at Pair Networks.

This is a reply from plesk about cgi recently on my cgi forms that were
working, stopped working, and somehow started working again without anyone
finding the problem:
>>>>>>>>>>>>>
"Actually root at localhost shouldn't work at all. The point is that qmail
unlike sendmail is unable to pass messages via the system mail delivery into
the /var/spool/mail/username file. It works only via SMTP. Please use an
actual mail address in your cgi scripts." 
>>>>>>>>>>>>>>

Since the ecommerce store is php and root at localhost has been working for
months is there someplace I can look to try to find the problem?

Thanks!

Sincerely,
Melinda Odom
www.designhosting.biz
479-471-0891


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