I will say this, and say it only once: It is a gross disservice to any user transitioning to a brand new platform to encourage them to use software that is out of support. It's just bad practice to use out of support software, period. And how much you like it is not relevant.
Thunderbird is a wonderful email client, fully accessible and fully in support, that runs fine under Windows 10. The Windows 10 Mail App is also accessible and more than adequate if you don't have need for what I'll call a "feature rich" email client.
I don't know of a single email program that doesn't have an import/export feature related to contacts. But in this day and age, if you're transitioning from a client that maintained its contacts strictly locally and within itself, you should establish an account that has IMAP access and to which email, contacts, and calendar can be synchronized across devices and even different email clients.
Brian - Windows 10 Pro, 64-Bit, Version 20H2, Build 19042
There are many who labor under the gross misapprehension that the Constitution is a cage and a laundry-list rather than a framework upon which great things have been and still will be built. Many things that are entirely Constitutional are not "in the Constitution," but are allowed under it.