I am receiving error on my all website.

"mail" statement of php can't work on every site.

mail($to,$subject,$message,$headers);

Mail statement we used for : Guest Book, First Mail to Register User, Forget Password, Order Confirmation and more...

Sites Name : speed4property.com, a1letters.com and more.

In php.ini:Remove `mail' ...

Any difference between PHP mail() OR SMTP mail. And which is the best for our server.

The SMTP settings are for when SMTP authentication is turned on from localhost, or is otherwise unavailable (say you send mail out through a different server) and you have to configure it to work differently than standard.

Safely ignore those settings, as it all runs through the php mail() function anyway.