unlike regular wordpress mails, JetPack adds a www. after the @.
I'm afraid I can't reproduce this on any of my test blogs. Jetpack doesn't modify the sender. It uses wp_mail() here:
https://github.com/Automattic/jetpack/blob/3.1.1/modules/contact-form/grunion-contact-form.php#L1403
The only way to change wp_mail()'s sender is through a filter, wp_mail_from:
http://codex.wordpress.org/Plugin_API/Filter_Reference/wp_mail_from
Jetpack doesn't use that filter.
I'd suggest looking at your other plugins to make sure you're not using that filter in any other plugin. You can also look at your site options under Settings > General to make sure you don't use www there.
Let me know how it goes.
