Email is inherently buggy and is generally a kludged together pile of broken outdated technologies and methods that were never meant to work like this and so publicly accessible, which is why the security/relaying options now are precariously added which is generally why it doesn’t work.
It’s not just email, look at HMRC integration and open banking,l both more unreliable than the old ways of doing things that were technically less secure. Browsers now block most useful functions and plugins to the point they constantly stop working to keep up with the latest practices. The technology moves forwards while the users take a step backwards.