Gmail and Yahoo are updating their mail requirements by extra checking with a feature called DMARC.
DMARC, which stands for Domain-based Message Authentication, Reporting, and Conformance,
-- is an email protocol that,
-- when published for a domain, controls what happens if a message fails authentication tests
-- the recipient server can`t verify that the message`s sender is who they say they are
For full details review the MXtoolbox.com discussion on DMARK and how to resolve many issues.
-- https://mxtoolbox.com/dmarc/details/what-is-dmarc

Do I need DMARC ?

In our opinion having green tick-marks against all aspects of email delivery will help your delivery rate. Not having it can cause issues.
Ensure your domain mail settings are up to date:
-- Set up SPF and DKIM email authentication
-- have a valid PTR for valid forward and reverse DNS records,
-- ensure that the DMARC quarantine enforcement policy is enabled and set to Quarantine
use MXtoolbox.com to verify your mail setup parameters, these parameters are very easy to configure and your email sending rate will improve.

[ -- link to Test your mail domain here : MXtoolbox.com ]