Thanks for posting this. It worked first time for me without a reboot. I have 3 mail accounts running through Outlook and 2 of them were fine, but the third wouldn't send. All 3 are now working properley.
I have exactly the same problem. All e-mails have disappeared from my VM inbox and only new ones appear in the Win 10 app. I hope a fix is out there to restore the mails.Is it as simple as deleting the account from the Win 10 app? I wonder.
The best advise I have about the Mail App in W10, comes from a Microsoft Beta Tester, who tells me that the mail app is 'Work in Progress', and don't use it. Do what I did and download the 'Windows Live package then just install 'Windows Live Mail' and use that. Getting rid of the W10 Mail app itself is a little more involved. You need to enter a special command in Windows Power Shell this one:-