I have two different university accounts (one as a student and one as an adjunct). These accounts have the university domain, but they are through Gmail. Last year the university also instituted Microsoft single-sign-on for all emails. Single-sign-on has the well-known, apparently unsolved, and extremely annoying problem that it makes it impossible to be signed into multiple single-sign-on accounts on the same browser at the same time. The solution to this problem so far is to use a private tab, or the Firefox "multiple containers" add-on, and separate one of the accounts into it's own container. Thunderbird seems to have the same problem. I cannot connect to both accounts at the same time. The second one will not even open the popup to give credentials, and will always claim invalid authentication. Is there some workaround similar to the Firefox browser workaround mentioned above?