Yahoo also wants OAuth or "enable legacy insecure apps"

[BjarniRunar]

Same problems as GMail.

We should ultimately add OAuth support for Yahoo.

In the near term, adding Yahoo to the static ispdb list, with hints that trigger the warning would be better than what we do now (nothing: the user just gets told their password is wrong).

[BjarniRunar]

It seems some sort of secret hoops must be jumped through for Yahoo to allow one to create OAuth accounts that can access mail: https://stackoverflow.com/questions/36058534/how-can-yahoo-mail-be-accessed-by-imap-using-oauth-or-oauth2-authentication

I doubt this will get fixed for 1.0rc1, but we can at least warn the user.