Can't send email from a POP client, error code 553
If you've recently added an extra email address to your Yahoo Mail account, but haven't verified it, you'll receive a 553 SMTP error code when you attempt to send email from a POP client.
Check out our steps to add or verify other email accounts in Yahoo Mail to fix this error.
Check your added account's mailbox - An email with steps to verify the account will be sent to the address. Once verified, you'll be able to send emails from it in a POP client..
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