@jerbalmya I can definitely provide me insight into this. Sending email via PHP is an extremely complex thing and unfortunately the vast majority of it is outside of Gravity Forms control and actually resides at the server and DNS level.
If you receive the notifications at your John.email@example.com email address but not when they are sent to a @fedex.com email address then a variety of things could be happening.
First it could be due to the fact the ip address associated with your web server is on a blacklist used by whoever manages @fedex.com email. If that's the case any email sent from your IP address is going to wind up in spam or possibly discarded entirely. This can happen with shared hosts where IP addresses are shared and one user has ruined it for the other users by causing the IP address to get blacklisted.
Second it could be due to the fact the web server and DNS is not properly setup to reliably send email. What your web host says is partly correct. It could be considered spoofing if the web server and DNS associated with the site aren't configured in such a way that it doesn't appear that the email is legitimate.
The second issue is the most likely cause. This means you would need to take some steps to make sure that email send via your web server is sent in a more reliable fashion so that it looks more authentic to email servers that are configured in an extremely secure fashion.
Some steps you can take include configuring SPF records for the domain of the web site so that at the DNS level it's saying your web server is allowed to send email on behalf of that domain name. Another thing you can do is then configure your WordPress site to send email via SMTP.
I would suggest reading this extremely good article by Joost de Valk:
This article discusses email reliability as it relates to sending email via WordPress. It's directly applicable in this situation because Gravity Forms uses the WordPress wp_mail() function to send email.
Look over that article AND discuss it with your web host if you are unsure how to implement what it suggests.
Gravity Forms itself can't send email. That is on your web server and it's completely out of our control as it's things that reside at the server level.
Also as Rob mentioned above it is very important that you configure the Send From to use an email address that is associated with that site OR associated with the SMTP settings you configure if you configure your WordPress site to send email via SMTP. This is discussed in the article I link to above.
Posted 6 years ago on Wednesday April 24, 2013 | Permalink