I find this very annoying too. When you get a lot of emails and use multiple timezones it is especially tiresome. I have no interest in emails that arrived on Thursday I want a real date and consistency. The concept of today, yesterday, Friday...Etc... then 28th... 29th... - it’s awkward and not business friendly. I have searched but been unable to find a way of turning on ‘all real dates’ even when using timezone support. It’s an issue in many Apps - Messages, Facetime but most annoying in Mail. It should be possible to turn on ‘absolute dates’ in General settings, Language and Region but it’s not.