Autoresponder adds "on behalf of"

When I set up an autoresponder for info@xtraclase.com the autoresponder gets sent, but in the FROM it says xtraclas@delta.dotanything.net; on behalf of; Equipo XtraClase.Com [info@xtraclase.com]

Is there a way to prevent the "on behalf of" ?

 

Nevermind, just found it. In Exim Configuration, just uncheck "Set the Sender: Header when the mail sender changes the sender (-f flag passed to sendmail)."