Yahoo and Hotmail Issues

Hi, We have a Free Classifieds WP site where users register for free and send each other messages.
We have “Postman SMTP Mailer” plugin Installed.

Issue?
User A: When User A (yahoo/hotmail) sends a message (via our site) to User B. Email will not be delivered to User B.
However when User A’s is a gmail or other emails, email will go through. We understand that this is due to Yahoo’s dmarc policy (which prevents SPAM)
As site admins, We know because whenever an email is not sent by a user, I receive a “Mail delivery Failure” on my ADMIN’s email notifiying us that an email was not sent.

Since All our out-going emails are authenticated with our server’s main email. In a normal scenario where an email is SUccessful; UserB will receive an email that show; User A’s email but is (via our server’s email)

Solutions?
* Some settings that needs to be changed on our CMS or Host?
* We should update the settings; When User B receives email it should NOT state the SENDER User A’s email. But must be an Admin’s Email; Because Yahoo rejects due to their DMARC policy. We should code in a “Reply-To” Field in the form which will states the User A’s email.

Any Idea What is the main issue?

Thanks
Lee