problem with html email sent from asp.net application

hi, 
 my application sends an email to a user. now the email body has a hyperlink, which shows as hyperlink to some recepients and as plain text to some other recepients. below is the code i used to send email from the application
string ToAddress = abc@123.com;
string FromAddress = def@123.com
link="<br>Please click the following link to look into the Information<br> http://forums.asp.net/AddPost.aspx?ForumID=18"

 MailMessage mm = new MailMessage(FromAddress, ToAddress);
 mm.IsBodyHtml = true;
 mm.Body =   link;
 mm.Subject = emailsubject;
SmtpClient smtp = new SmtpClient();
smtp.Send(mm);
 can someone please tell me where i'm going wrong?
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