In ec_mail.module,v 1.1.2.16.2.19 2008/07/16 01:29:43 davea Exp $
on line 840:

'#value' => t("<p>The message shown below is to be sent from %from to %to. You can take this opportunity to modify the message before sending it.</p>", array('%from' => $mail['from'], '%to' => $to)),

should be:

'#value' => t("<p>The message shown below is to be sent from %from to %to. You can take this opportunity to modify the message before sending it.</p>", array('%from' => variable_get('site_mail', ini_get('sendmail_from')), '%to' => $to)),

i.e. $mail['from'] is undefined at that point in the code.