If in case you have trouble to attach the file or folder on Yahoo mail, you can try these given steps for troubleshooting.
When you follow all the steps and still not able to fix the problem then you can ring the Yahoo mail customer care number which is 365x24x7 available for troubleshooting.
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If you want to know how to sign in the Yahoo mail through the Mail app, you should follow the way given here. In case of trouble, you can contact customer care executives.
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