Error 553 while sending email from a POP client
Unverified email addresses you attempt to send from will cause this error. Use these steps to verify the address.
- Sign in to Yahoo Mail.
- Mouse over the Settings menu icon , then select Settings.
- Click Add beside "Accounts."
- Enter the email address and a description.
- Click Save.
A verification email will be sent to the address. Follow the email's instructions to verify the address, then you'll be able to send emails from it in a POP client.