According to the documentation and the available examples, it is possible specify the "from" address using either mailSend or fromDeveloperId. Starting with version 2.1, using fromDeveloperId leads to the following error:
[INFO] Invalid mail sender: name and email is mandatory (null (null)).
Looking at the source code, the regression seems to have been introduced by adding "@parameter expression="$
"" to the declaration of the mailSender attribute.
Attached is a patch fixing the issue from the svn repository at revision 727375.