Upfront contact form not working

Hello!

I've been trying to use the contact form on Upfront with no success yet

The form shows a "success" message but no email is ever sent. I've tried in WP installs in both MediaTemple's GRID and WiredTree's VPS with same results.

When taking a look at the "mail queue manager" in WHM I saw this error when using a gmail address as the form recipient:

"Diagnostic-Code: smtp; 550-5.7.1 Unauthenticated email from yahoo.com is not accepted due to
550-5.7.1 domain's DMARC policy. Please contact the administrator of
550-5.7.1 yahoo.com.br domain if this was a legitimate mail. Please visit
550-5.7.1 https://support.google.com/mail/answer/2451690 to learn about the
550 5.7.1 DMARC initiative. y24si6213060ita.13 - smtp"

(yahoo.com was the domain of the email used in the contact form; the form was set to send the message to a gmail address)

So I tried using Amazon SES to deliver the emails and got an error (it sends WP internal emails just fine though). It seems the contact form uses the visitor's email as the "from" so Amazon doesn't recognize it as a verified sender (and gmail doesn't accept the email either because it looks like spam!).

How can I solve this?

(I have already granted support access)

Thank you very much!