How can i fix Yahoo Mail Down issues? When will Yahoo Mail be fixed?
In order to fix your Yahoo Mail Down issues, you can easily get in touch with the Customer support team. And make sure you click on the link and contact Yahoo mail technical support team. Sometimes due to some technical or backend work going on Yahoo website or when you have a bad internet connection then in these cases also, you can not avail Yahoo’s free mail services. And you should wait for some time.

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Jim Wick commented
If you are unable to send mails:
Emails that have sent successfully will appear in your "Sent" folder, so check that first. If it's there, it's been sent.
If the email isn't there, check your "Drafts" folder — maybe you didn't actually send the email like you thought you did.
Double-check the spelling of the recipient's email address to make sure you've sent it to the right person. Also make sure that you haven't blocked their address.
Lastly, ask the recipient to check their own Spam folder, filters, and blocked addresses list to ensure that your email didn't hit any walls on its way to them.
Cheers,
Jim Wick