Make text bold in the email content generated through UDF

All,

I am generating an email thorugh UDF by invoking a Mail channel. The scenario works fine, however it's the minor cosmetic issue that is bothering me.

Code used is mentioned below. In this how do I make some parts of the content bold and underlined. I have tried <b></b> but that does not work. For example in this XML below, how do I make strFieldName bold and lets say "is  missing" underlined.

String smtpXML ="<?xml version=\"1.0\" encoding=\"UTF-8\"?>"

+"<ns2:Mail xmlns:ns2=\"Mandatory" _mce_href="http://sap.com/xi/XI/Mail/30\"><Subject>Mandatory">http://sap.com/xi/XI/Mail/30\"><Subject>Mandatory Field Missing</Subject><From>xyz@xyz.com</From><To>xyz@xyz.com</To><Content>"

+"Dear User,\n\nMandatory Field '"+strFieldName+"' is missing. "+ "Please find below the interface details"+"\n\nInterface Name: "+headerField1+"\n\nInterface NameSpace: "+headerField2+"\n\nSender System: "+headerField3+"\n"+"Receiver  System: "+headerField4+"\n\nPlease populate all the mandatory fields and resend the message.\n\nRegards,\nPI Team. </Content></ns2:Mail>";

Thanks.