You might just be making some small mistakes. 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 or you are encountering yahoo mail not working issues, then 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. Use these instructions to solve yahoo mail not working on android issues.