It is currently not possible (without altering the tld) to send an email to an arbitrary email address because the to attribute is set to not accept expressions. It might be useful to enable rtexprvalue on the to attribute. (I understand that it might be a security problem to set this to true)
If you want to send the e-mail to an address that is figured at runtime or to an address that is not static, use the body of the setRecipientTag.