I have a feeling this is directly assigned to BlueHost. Their support is quoted as such:
"I wasn't able to see a "from address" on that email header information. Months ago we made a change to our system that forces all email sent from our customer accounts to be checked for spoofing. Due to this measure, you can no longer send emails that appear to be from an email address that is not on your account.
Therefore, if you have a contact form or email program that attempts to set the "From:" header to anything but an email address that exists in your bluehost account, the mail will be rejected by our spoofing filter.
If you are sending email through SMTP, you must connect to "localhost" to send your email. Remote SMTP connections are no longer allowed from our servers and you must use AUTH when you connect to the SMTP.
Lastly, there is only one other change you should be aware of. Our mail system will not allow this header:
From: email@domain <email@example.com>
Even if the email is valid, our system will fail the message due to the double declaration of the email address.
Please check your script and ensure that these requirements are being met by your script. If you feel that your script meets these requirements and it's still failing, we will be happy to examine it for you. Please just provide the script code and a way to test the issue so we can troubleshoot."