Comment by signal11

Microsoft Mail is a product from the early 90s for DOS/Classic Mac OS. Microsoft Internet Mail was a logical upgrade, then added support for newsgroups. Eventually, after the success of Outlook in the MS Office world, it rebranded to Outlook Express. You could still see echoes of Microsoft Internet Mail and News if you looked hard at Outlook Express, its executable was called msimn.exe.

Windows Live Mail and Windows Mail were essentially newer, Vista-era versions of Outlook Express. It's the same program rebranded. Mail was bundled with Vista, Live Mail was a way to push the Live branding and get the newer program into the hands of those running older versions of the OS (WinXP).

Microsoft Outlook is a different beast with a different lineage, part of MS Office, and can be thought of the "pro" version of the basic mail clients bundled with Windows.

Yes, Microsoft could probably do with some branding discipline but the technology is quite predictable.

I'm not sure what Mail.app is, I always thought that was Apple's. Entourage was IIRC a native 'designed for Apple' PIM that eventually made its way into Office for Mac, eventually they decided to rationalize and have one client -- Outlook.

Hotmail / Outlook.com - Outlook.com, again despite the confused branding, is Hotmail evolved. Over time, Microsoft slowly merged its consumer (Hotmail, Windows Live) UI with its 'pro' UI (Outlook for desktops, Exchange Web) so that these days they are all pretty similar. These days you also have Outlook's mobile apps for Android and iOS and those too have a familiar look and feel.

I don't see any of these as a bad thing. Microsoft's history is linked to the history of personal computing and the ebbs and flows of market forces that shaped the PC biz and continues to shape today's technology. Given all the churn in this space, it's actually kind of awesome how their technology has evolved -- and will continue evolving, e.g. with all the focus on a web version of Office. But yes, their sudden shifts in branding is pretty sucky and they could do a lot better there.

But "none of them 100% work" is pretty harsh. No mail client is right for every use case (except emacs, naturally -- if it doesn't work for you it's because you haven't written enough elisp yet). But these are very widely deployed products and do work for a good segment of their target market.