When it comes to sending and receiving emails, there are a few things that you need to make sure you have set up in your DNS in order to guarantee email flow.

Email Best Practice Recommendations

SPF

Set up SPF to help prevent spoofing | Microsoft Learn

Define your SPF record—Basic setup – Google Workspace Admin Help

DKIM

How to use DKIM for email in your custom domain | Microsoft Learn

Turn on DKIM for your domain – Google Workspace Admin Help

DMARC

Use DMARC to validate email, setup steps | Microsoft Learn

Add your DMARC record – Google Workspace Admin Help

Email Security

If you do not use any kind of security/spam system, I would suggest using Proofpoint. Email security, encryption, and more.

Proofpoint, Inc. is an American enterprise cybersecurity company based in Sunnyvale, California that provides software as a service and products for email security, identity threat defense, data loss prevention, electronic discovery, and email archiving.

Proofpoint – Texas Fixer