Three weeks ago (11/08/2020) our OAuth registration at the Yahoo Developer Portal became misconfigured, so a Yahoo! account could not be set up via Automatic setup. We have contacted Yahoo Developer support to resolve the issue and they finally fixed the registration for eM Client.
Because some permissions were renamed by Yahoo! a new version of eM Client is required.
Please download the fixed version from this article:
https://forum.emclient.com/t/fixed-yahoo-accounts-and-em-client/67260
After you install the update, please go to Menu>Accounts and set up your Yahoo! account using the Automatic setup.
We apologize for the inconvenience.
We are sorry for any inconvenience in the meantime.
In case of an urgent issue please reach out to use directly at [email protected]