Protect your email with SPF (sending control) and DKIM (spoof control) – when hosting with O365 Email.
How to use DMARC to Validate Email: https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/use-dmarc-to-validate-email?view=o365-worldwide
How to use DKIM to validate outbound email: https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/use-dkim-to-validate-outbound-email?view=o365-worldwide
NameCheap – How do I add TXT/SPF/DKIM/DMARC records for my domain?: https://www.namecheap.com/support/knowledgebase/article.aspx/317/2237/how-do-i-add-txtspfdkimdmarc-records-for-my-domain/
Setting Up DKIM with Namecheap: https://help.sharpspring.com/hc/en-us/articles/115002810792-Setting-Up-DKIM-with-Namecheap
WordPress – WP Mail DMARC check: https://wpmailsmtp.com/how-to-create-dmarc-record/#check-dmarc