Mail is always "Downloading Messages".

I'm sticking my fingers down my throat at this response to a perfectly legitimate question by ggerritis, with whom I have complete sympathy. For a number of years now I have had similar issues when first opening Mac Mail on a number of different Mac computer's but this never happens on Windows email clients upon which I don't have any particular love for - so this is not a Windows promotion by any means. There has definitely been something wrong with Mac Mail over several versions on different releases of Mac OS X (mac OS) from at least Maverics through to El Capitan and maybe Sierra as well whereby despite every attention to detail regarding setting up accounts there are still a few (not always the same on each different computer) accounts that absolutely refuse to abide by the user deliberately deselecting "include when automatically checking for new messages" which is a very obvious plain English statement that the user should expect to function exactly as it says period, or as we have said in the UK for centuries "full stop". There is obviously a random bug in Mail software, so please do not insult users intelligence by using nice sounding corporate spin excuses and fobbing people off into a false wild goose chase. What is the point of including a perfectly obvious option if it systematically refuses to carry out the function as described. Let's have the truth for once and an honest answer that there is absolutely an issue and that it has been recognised and that is being seriously looked into.