okay here's my experience, I installed Windows 10 insider preview build 10122 and then checked out the new mail app. I switched my to microsoft account on my computer and I added an outlook account and a gmail account to the mail. The google account has no
problems in syncing at all but the outlook account was not syncing at all. And then I checked that it wasnt syncing on my windows phone too. I thought deleting the outlook account and logging in again would solve the problem but there was no option to delete
the account from mail!! I mean what the heck?!! I could delete google account though.
This problem persisted to all calendar and people apps too. I thought may be the microsoft account on my PC was not allowing it to delete. So I switched to local account and checked
if the delete option was there, but it wasnt. There would appear an error on the mail app that something is wrong with the account and gives me option to "fix it" and when I press that a window would open and crash, nothing happens( buggy mail app).
Then I tried changing my password so that I thought maybe at least it would prompt me to renter my credentials. When I changed my password, my phone asked to enter with new credentials,still nothing changed even after doing that and the PC remained to ask
to FIX it which does NOTHING.
Then I rolled back to Windows 8.1, in hope that they would work. I was on a local account on Windows 8.1 and then If I go to mail, it
asks me to check my network connection, and in store it says it couldnt sign me in, bad length. MS has officially messed up my outlook both on my PC and phone.
I still dont have solution for this and if I try to switch to Microsoft account from my local one it says it cant connect to Microsoft services.