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How to Fix Error Code 550 Mail Box Unavailable in Yahoo


550 Error generally refers to the SMTP error codes in which a user’s outgoing emails are not delivered to the recipient. When facing Error 550 Mailbox Unavailable or any similar Error 5xx in ynded to avoid sending email flagged with a 550 or other 5xx error code. This problem generally occurs because:

  • You are trying to send emails to an invalid email address.
  • Your IP address has been listed on a Block list in Spamhaus.
  • Your email failed authentication checks against your sending Domain’s DKIM or DomainKeys policy.
  • Your SMTP connection was declined.
  • Your email includes content which is restricted as per Yahoo policy.

Suggestions to Fix Error 550

1.) You must be an administrator of server in order to fix the problem.

2.) If you the error is consistently appearing for more than 48-hours period and you have already given ample time to fix the error, it is best to go through the following practices when sending email through your Yahoo Mail account.

  • Have a policy for removing email addresses that result in errors/bounces.
  • Make sure to have a good email sending reputation. This is because Yahoo reviews IPs submitted for delivery issues, and based on which they may alter your reputation in their system.
  • Fill a new sender application via below mentioned link to discuss your issue. Click here
  • However, even if you have a good email sending reputation, users can vote your email as spam, and which can affect your reputation, resulting in such errors.
  • Make sure that spammers are not abusing your email server.
  • If you using a shared IP address, mail traffic from other domains may impact your IP sending reputation negatively.
  • Make sure to consider following when you are reviewing your outgoing emails for objectionable content or practices:
    • IP address reputation
    • URL reputation
    • Sender reputation
    • Domain reputation
    • DomainKeys identified Mail (DKIM) signatures.
    • Domain-based Message Authentication, Reporting & Conformance (DMARC) authentication.

Ways to Improve your Sender Reputation

  • Follow the best practices for bulk email senders.
  • Apply for new sender status if you are a bulk email provider.
  • Know about sending limits in Yahoo Mail (on official website).
  • Review SMTP error table (on official website).
  • Make sure your emails meet industry authentication standards.
  • Review Yahoo terms for information on policies.

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