How to validate email address using RegularExpressionValidator?

If you want your email address to be a mandatory field, write following code.

               
<asp:TextBox ID="txtEmail" runat="server" />
<asp:RequiredFieldValidator ID="req4" runat="server" ControlToValidate="txtEmail" Text="*" />
<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ErrorMessage="eg. you@domain.com" ControlToValidate="txtEmail"
                    ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*"></asp:RegularExpressionValidator>

If you do not want email address as mandatory field write following code.

<asp:TextBox ID="txtEmail" runat="server" />
<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ErrorMessage="eg. you@domain.com" ControlToValidate="txtEmail"
                    ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*"></asp:RegularExpressionValidator>

This will only validate the textbox for correct email id format if something has been entered otherwise no validation will be done as there is no RequiredFieldValidator used in this code snippet.

Thanks