Use a string for the url and then concatenate with other content. Check below..
string strBody="";
string EMAIL="test@test.test";
string myURL = "http://www.testweb.com/testpage.aspx?eml=" + EMAIL.ToString();
strBody = strBody + "Date: <strong>" + DateTime.Now.ToShortDateString()+ "</strong><br><br>";
strBody = strBody + "<a href=" + myURL + " targer= _blank>click here</a>";