my user creation coded email goes to everyone's spam folder

hey guys, i'm using the below code at the last step of my createwizard for useraccounts, to send an email to the user with a confirmation link. works fine, except that it goes straight to the junk folder of everyone i've asked (outlook2k3, yahoo, gmail - users) - i tried copying the exact subject format of a site i know doesn't have this problem, but that didn't help too much.
am i missing something that'll make the email sound more secure to receiving mail servers? some header or something? the below code is what i'm using now:
    protected void CreateUserWizard1_CreatedUser(object sender, EventArgs e)
    {
        CreateUserWizard cuw = (CreateUserWizard)sender;
        MembershipUser user = Membership.GetUser(cuw.UserName);
        Guid userId = (Guid)user.ProviderUserKey;
   ...