From looking at Mail::Mailer, the way that you are setting the "MAIL FROM" address doesn't work. Mail::Mailer constructs the address and doesn't look at the From: header or the 'MAIL FROM' header. It does look at the MAILADDRESS environment variable. BTW, you should set the Return-Path header. That is set by the receiving MTA.
You could set the environment variable before sending the message.
$ENV{MAILADDRESS} = $$siteMessageFrom;
$mailer->open(\%headers);