http://blogs.msdn.com/b/mstehle/archive/2010/03/10/howto-return-to-sender-transport-agent-sample.aspxThis transport agent identifies a message it wants to reject by looking for “[TEST]” in the subject.&#160; If it finds a message to reject, it creates a new message to be sent back to the sender and attaches the original message being rejected to theen-USTelligent Evolution Platform Developer Build (Build: 5.6.50428.7875)http://blogs.msdn.com/b/mstehle/archive/2010/03/10/howto-return-to-sender-transport-agent-sample.aspx#9976834Thu, 11 Mar 2010 13:34:03 GMT91d46819-8472-40ad-a661-2c78acb4018c:9976834Matt Stehle - MSFT<p>Actually, I wasn't aware that had changed in Framework 3.5 but you are right - str1 + str2 is in fact equivalent to String.Concat(str1, str2) now. &nbsp;I've always been in the habit of using String.Format and String.Concat due to the inefficiences of adding strings with the '+' operator pre-3.5. &nbsp;</p> <p>Since it's all the same in the IL there's really no performance value. &nbsp;I guess using '+' is a bit more readable maybe I'll use that in the future.</p> <div style="clear:both;"></div><img src="http://blogs.msdn.com/aggbug.aspx?PostID=9976834" width="1" height="1">http://blogs.msdn.com/b/mstehle/archive/2010/03/10/howto-return-to-sender-transport-agent-sample.aspx#9976526Wed, 10 Mar 2010 22:45:35 GMT91d46819-8472-40ad-a661-2c78acb4018c:9976526Duncan Smart<p>String.Concat? Really? FYI: str1 + str2 compiles down to a String.Concat anyway and is a lot more readable!</p><div style="clear:both;"></div><img src="http://blogs.msdn.com/aggbug.aspx?PostID=9976526" width="1" height="1">