3769507 - Outbound emails bounced with SMTP 5.7.26 (unauthorized sender)

Outbound emails are bounced (SMTP status code 5.7.26) despite relaxed DMARC alignment and maintained DNS records.

SAP Service Cloud Version 2

No specific steps to reproduce were provided.

The receiving server rejected the message with SMTP 5.7.26 because the sender was unauthenticated.

1. Verify SPF: Confirm the SPF DNS record authorizes the outbound sending server/IP and that the envelope sender (Mail-From/Return-Path) passes SPF.
2. Verify DKIM: Ensure outbound emails are DKIM-signed and the corresponding DKIM selector DNS record is correctly published and validates.
3. Confirm DMARC: Ensure the DMARC record is correctly published. Even with relaxed alignment, DMARC requires SPF or DKIM to pass.
4. Configure a custom Mail-From domain for the email channel to improve authentication handling as per product guidance.
5. Check receiving domain restrictions: Ask the receiving domain administrator to review any blocklist/restriction rules that may classify the sender domain or the service as unauthorized.
6. Retest outbound email after applying the changes.

• refer to: Configure custom Mail-From domain
• refer to: SAP Note 3433341 - Resolving outbound email blocking issues in Service Cloud v2

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