Hello!
I noticed today on two different 2011 MacBook devices (High Sierra) that the Mail email application does not synchronize the mailbox (my default iCloud account), in the top right corner a dark triangle with an exclamation mark and the text "Account Error". No problems with the Internet in general, everything works perfectly on both computers, both wired and wifi.
Please help!
MacBook Pro 13″
You probably enabled multifactor authentication on your iCloud Account. iCloud account passwords on pre-Sierra 10.12.4 will need to be followed up by the multifactor authentication code that appears on your iPhone, iPad, or AppleTV when logging in on the older Mac.
So if your password is Password1234! (this is not a recommended password, as it is a dictionary password and too obvious, no passwords should have any dictionary words. Substitute numbers and funny charaters for various letters to make your password more secure), and the code appears on the screen of 5429, you would enter Password1234!5429 instead.
Multi-auth is default in iCloud so this is not a problem, I've use this account since years ago without any problems - and of course with hard password usage - until yesterday when Mail randomly shows me that triangle with the error message over the days. After some times it just works but I don't know whats happening there.
If it works intermittently, it could be a problem with too much traffic on the server.
I would start looking for another email provider.
Any email where you can setup IMAP is good, because you can setup on multiple devices.
Mail problem
