Contact Form – What Mail Function is used?

Jetpack, like other contact form plugins, uses wp_mail to send out emails.

I’m not sure how Mailpoet works, but you can check if that function works properly by leaving a comment on your site and checking if you receive an email. Another alternative would be to use this plugin:
http://wordpress.org/plugins/check-email/

If you find issues with that function, you could use a plugin like this one to configure your WordPress installation to use a specific email service:
http://wordpress.org/plugins/wp-mail-smtp/

If the function appears to be work properly, it means that Jetpack’s emails are filtered out before they can reach your inbox:

• They can be filtered out by your server before they even get sent out; your hosting provider should be able to check their server email logs to find out if the emails were blocked.
• They can be filtered out by your email provider. If you don’t find the emails in your spam folder, you might want to try to send out Jetpack emails to another email address, and see if you keep experiencing issues. You can do so thanks to this option in the contact form builder:
  http://jetpack.me/support/contact-form/#jp-carousel-723

Let me know if this helps.

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.

Could you let me know what your site URL is, so I can take a closer look?

If you want it to remain private, you can also contact us via this contact form:
http://jetpack.me/contact-support/

Thanks!

I’ve just replied to your email. Let’s continue the conversation there!