If you get the following error while accessing FormMail in a cpanel server,
Premature end of script headers: /usr/local/cpanel/cgi-sys/FormMail.cgi
Make sure the file FormMail.cgi has 755 permission and ownership as follows:
-rwxr-xr-x 1 root wheel 1219000 Aug 3 03:52 FormMail.cgi
You can use the following commands to correct the ownership & permission.
chown root.wheel /usr/local/cpanel/cgi-sys/FormMail.cgi
chmod 755 /usr/local/cpanel/cgi-sys/FormMail.cgi
JFYI: ‘cgi-sys’ folder should have 751 permission and root.wheel ownership.