The ‘550-5.7.26 This mail is unauthenticated’ error indicates that for the given message, DKIM checks did not pass, and the SPF check for the specified domain failed as well.
When Gmail identifies an email as unauthenticated, it signifies a potential security risk both for the sender and the Gmail users. Emails that aren’t validated using either SPF (Sender Policy Framework) or DKIM (Domain Keys Identified Mail) are likely to be rejected by Gmail’s strict filtering mechanism.
Resolving the Error – Solution
To address this error and ensure your emails are not rejected by Gmail, follow these steps:
- Authenticate Using SPF: Ensure you have a valid Sender Policy Framework (SPF) record for your domain. SPF helps email servers recognize if the mail originates from a trusted source associated with the domain.
- Configure DKIM Signing: DKIM (Domain Keys Identified Mail) adds an encrypted signature to your emails, which is then validated by the receiving server. Make sure that DKIM signing is configured and activated for your domain.
- Refer to Google’s Authentication Guide: If you need detailed instructions or encounter issues during the authentication process, check out Google’s guide on configuring DKIM and SPF authentication.
- Contact Support: If you’re still facing challenges, consider reaching out to your email provider’s support for specialized help.