That might be from a Microsoft feature to prevent phishing that blocks display name spoofing. I get hit with that when I email from my personal to work email… the display name portion of the FROM address matches my work so it trips this filter.

Obviously they can only do this for unique-enough names and so this filtering could never work for “Joe Miller” but it does stop the dozens of phishes we see per day that are FROM our CEO’s first and last name but with a Gmail email address.