Hi and thank you for your question.
Please do this on the iPad now:
First, tap on the Settings app, and then scroll down the left and tap "Mail, contacts, calendars."
On the right, tap your Yahoo account listed, and then tap "Delete account" at the bottom.
Next, go back to "Mail, contacts, calendars" and then tap "Add account."
Select Yahoo from the list of options, and then fill in your account email address and password, and tap Next > Done at the top-right.
Finally, re-open the Mail app; do the emails come in all right this time?
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