email validation

[k0r54]

Hi, i was wondering if some1 could tell me the code to validate an email for incorrect charactors.
I believe it is something like this but i am not to sure

  if (ereg('^[a-zA-Z0-9_\.\-]+@[a-zA-Z0-9\-]+\.[a-zA-Z0-9\-\.]+$', $address))
    return true;
  else 
    return false;
} 

also how can i check for certain fields to be field in. i.e my form has 4 text fields ($name,$message,$email,$contact number)

i want name,message and email to be filled in but contact number is optional. i cant figure out how to exclude contact number

Thanks Adam