Most Yahoo Mail issues are caused by invalid settings or something wrong with the Yahoo Mail account that you're trying to add. So, if your
Yahoo Mail not sending on iPhone, move to the iPhone settings. Then, tap on "Mail" to view mail settings. Now, tap on the "Accounts." Then, tap on the Yahoo Mail account. Now, tap on the email account again, and in the "Outgoing Mail Server" section, tap on "SMTP." Tap on the "Primary Server" section (it should say "On" to the right). Verify the "User Name" field that is has listed the full email address. Now, type your password again in the "Password" field and tap on the "Done" button.
