For a second time, I opened windows 10 mail to find my main email account no longer listed. The inbox shows email sent to that account although I can or was able to read the my mail using the ISP's internet based mail package. The last time I added the account and windows 10 mail reloaded all the mail folders from the ISP - a long process. Switching to my Hotmail.com account treated that email normally. Earlier today I performed a restart which may or may not caused this. The first occurrence may have occurred after OS upgrade and restart. Any help is welcome.