Some customers using Rebel Cloud Email encountered issues when attempting to send email via external providers, such as Gmail or Yahoo, using the “Send As” feature.
Affected users received bounce-back messages stating: “550 5.7.1 Authentication Refused – OXSUS003_207”, which indicated their messages were being rejected during SMTP authentication.
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Cause:
A temporary configuration change within our outbound email authentication system led to legitimate SMTP sessions being mistakenly flagged and rejected. This specifically impacted users sending email through third-party platforms that authenticate using Rebel Cloud Email credentials.
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What We Did:
Our engineering team worked with our email infrastructure provider to review and resolve the underlying authentication layer issue. As of 9:30 AM EDT, the error has stopped occurring and affected services are back to normal.
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Next Steps:
We will continue monitoring for any further anomalies and are implementing additional safeguards to ensure external SMTP connections are correctly processed without disruption.
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What You Can Do:
If you previously experienced bounce-back errors when sending via Gmail, Yahoo, or other external apps — you may now try again. The issue has been resolved.
If you continue to receive errors, please contact our support team with a copy of the message for review.
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We sincerely apologize for any inconvenience this caused, and we appreciate your patience as we worked to restore full service.
We are currently investigating an issue affecting **outbound email delivery** for clients using third-party email platforms like **Gmail**, **Yahoo**, or similar services via the “Send mail as” feature.
Some users have reported bouncebacks or failed sends with the following error: