I can imagine that some race condition slips into production, but what's hard for me to process is why it’s 5 or 6 years later and it’s still not fully fixed.

I mean, even if you have no idea what's the cause, you e.g. stuff counters everywhere and when they don't match you send the telemetry with the details. Privacy is preserved and over time you get an idea what to look for.

I admit I have no idea how mail client works, but clearly there must be some way they could pinpoint it, with such large userbase..

> but what's hard for me to process is why it’s 5 or 6 years later and it’s still not fully fixed

Because Apple's (the company's, as a whole) bug -> triage -> engineering -> deployment process is fundamentally broken, and obviously has been for decades at this point.

Say what you want about MS, but at least critical issues that actual customers are experiencing tend to get fixed.

Apple seems to have some weird 'maybe someone will look at it, if they have time, after they get done implementing new features for the next release' process. (Glaring example: daisy chaining DisplayPort support)