Adi Robertson, The Verge:

Apple has restored the email app BlueMail to the Mac App Store after its developer began a campaign to rally small developers. Blix, founded by brothers Dan and Ben Volach, has been locked in conflict with Apple for several months. It alleges Apple stole its anonymous sign-in feature for “Sign in with Apple,” then kicked it out of the App Store on flimsy pretenses to suppress competition. Apple, conversely, has said it removed the macOS app for security reasons.

From Apple’s point of view:

Apple has denied that its standards were inconsistent. “The App Store has a uniform set of guidelines, equally applicable to all developers, that are meant to protect users,” said the company in a statement. “Blix is proposing to override basic data security protections which can expose users’ computers to malware that can harm their Macs and threaten their privacy.” A spokesperson says that last week, Blix submitted a new version of its app that respected Apple’s Gatekeeper security software and resolved technical problems, including an issue that produced privacy and security warnings for users at launch.

Apple does take Gatekeeper seriously. In addition to Gatekeeper adherence, a new policy requires apps to go through a notarization process, where the developer uploads their app and it is scanned for malware. Hard to know if this is a developer not following protocol, or something deeper, perhaps connected to Blix suing Apple.

Blix fought their battle with Apple in public. You can read their side of this on the Bluemail web site.