Identify your domain extension in Yahoo Mail
You can now create an account with a different Yahoo domain other than @yahoo.com by selecting "@myyahoo.com" when creating a new account ID from the sign up page.
The domain extension is the ".com" part of your email address. While Yahoo accounts can end in "@yahoo.com" or "@myyahoo.com", some older accounts may have a different extension depending on the location where they were created.
If you have a Yahoo ID with a different local domain, like "@yahoo.co.uk" or "@yahoo.fr", make sure you include the correct domain extension when giving out your email address. If an email is sent to the wrong domain, it won't be delivered.
Find out what your Yahoo domain is in Yahoo Mail settings.