Graham60,
This forum post is about the email Microsoft sent out on December 11 regarding d-Mail.msp described in KB3093594. Understanding this situation is important to Windows users.
In my opinion it would be best not to clutter this thread with pros and cons of Microsoft's strategies.
Apparently, Microsoft is discontinuing the support of DeltaSync protocol which is currently used by Windows Essentials Live Mail 2012. This would be like the time about 6 years ago when Microsoft discontinued support for WebDAV and Outlook Express.
My assumption is that Microsoft plans to simplify its email/calendar/contacts technology and offer a single technology based on Microsoft Exchange and the Exchange ActiveSync protocol. This differs from Microsoft's previous strategy of the last 20 years
of having one email product for home-customers and a different email product for business-customers.
I haven't used Thunderbird in quite some time - but, I don't believe it supports Microsoft Exchange.
So, Internet Message Access Protocol and Thunderbird doesn't address that issue - and, really doesn't seem like a long term strategy if you are interested in using Windows 10 and other Microsoft technologies. Microsoft Exchange is a huge and varied set
of technologies that has far reaching impact on Microsoft customers.
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Update:
I researched using Thunderbird with Exchange Server. For the vast majority of Windows users, I would not recommend trying to do that. Most Windows users need a simple, straightforward solution.
Wikipedia: Thunderbird is an email, newsgroup, news feed, and chat (XMPP, IRC, Twitter) client. The vanilla version is not a personal information manager, although the Mozilla Lightning extension adds PIM functionality. Additional features, if needed, are
often available via other extensions.