A potentially dangerous Request.Form value was detected from the client

Hello Guys,

i got this error, while submitting a request on my website that had an email that was enclosed in <> marks, when i removed it, it worked.

pls advice
Ehi
Server Error in '/' Application.


A potentially dangerous Request.Form value was detected from the client (ctl00$ContentPlaceHolder1$Message="...yahoo.com,<xyz@yahoo.c...").
Description: Request Validation has detected a potentially dangerous client input value, and processing of the request has been aborted. This value may indicate an attempt to compromise the security of your application, such as a cross-site scripting attack. You can disable request validation by setting validateRequest=false in the Page directive or in the configuration section. However, it is strongly recommended that your a ...