Here are some links to check your @domainname.com
Here are the tools I used.
https://dmarcly.com/tools/ and the DMARC checker https://dmarcly.com/tools/dmarc-checker
You may also want to see this https://mxtoolbox.com/SuperTool.aspx
If you are sending emails from your own domain, you need to check this ASAP.
And if you were sending emails through an email service like Constant Contact, you need to stop sending emails from Gmail or Yahoo right away.
Ignoring this will inevitably mean your emails, not giving to your clients or prospects at all. So pay attention!
P.S. The good news is, your competition will ignore this. If you do it, you’ll win on the email marketing front.