You can try somthing like this to mak your mail body nice ...... :D
string GetBody()
{
string PreDefinedMailFormat = @"<html>
<head>
<title></title>
</head>
<body>
<div>
<span style='font-size:12px;'><span style='font-family:verdana,geneva,sans-serif;'>Hi {1} {2},</span></span></div>
<div>
</div>
<div>
<span style='font-size:12px;'><span style='font-family:verdana,geneva,sans-serif;'><strong>Congratulations!</strong> {0} has received and accepted your invitation.</span></span></div>
<div>
</body>
</html>
";
string MailReceiverFName = "Moumit";
string MailReceiverLName = "Mondal";
string MailSenderName = "KAKA";
string MailBody = string.Format(PreDefinedMailFormat, MailSenderName, MailReceiverFName, MailReceiverLName);
return MailBody;
}