If this is a problem, it applies to my previous El Capitan as well as my present masOS Sierra. Intermittenly, when I "light" up my computer (MBA), I get a popup window say one of my email accounts requires my password. For no real good reason, I have Gmail, Outlook, AOL, Yahoo and iCloud accounts. The popup window randomly can be any one of these accounts. Wondering if this is come kind of security problem with the email servers or some security setting with both El Capitan and Sierra? I'm slightly worried that it may be some malware that is doing this. I almost never reenter my password in these popup windows. Instead, I open up Preferences/Interent Accounts and enter my password(s) there. When these popup windows asking for my email passwords appear, in "Mail", the account is "down" until I reenter the correct password.