There is no special header information wich is requered by a webbased e-mail service, hence the only thing wich you can try to detect on is the from adres, specificaly the domain-name in the from adress.
If you're asking for technical help, please be sure to include all your system info, including operating system, model number, and any other specifics related to the problem. Also please exercise your best judgment when posting in the forums--revealing personal information such as your e-mail address, telephone number, and address is not recommended.
header detection