There are many ways in which you can improve the security of your Exchange Online environment. In this article, Sean McAvinue details the most important steps that admins can immediately implement to align Exchange Online tenants with a good security baseline and posture.
In this post, Microsoft MVP Alan Byrne explains how to configure the two most effective technologies that will ensure your outgoing email is successfully delivered. These technologies are known as Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM), and they protect your outgoing emails from being marked as spam while also flagging and blocking any incoming messages from unauthorized servers spoofing your domain.
A recent increase in email spoofing false positives causing legitimate email to go to Outlook junk folders can be explained by a change in Office 365 Advanced Threat Protection.