Email send receive issue

 Hi Upendra,

Based on the bounce message, Microsoft 365 successfully transmitted the email to Gmail. However, Gmail rejected the message with the error:

550 5.7.1 Gmail has detected that this message is likely suspicious due to the very low reputation of the sending domain.

The message authentication checks (SPF, DKIM, and DMARC) passed within Microsoft 365, indicating that the message was sent successfully from Exchange Online. The rejection was performed by Gmail's filtering system based on the reputation of the sending domain.

As the message you included provide, please contacting your administrator to perform a detailed review of the sending domain's reputation and email authentication configuration. Although the message passed through Microsoft 365 successfully, Gmail's response indicates that the domain itself currently has a low reputation in Google's filtering systems.

The administrator should verify that:

• SPF records are correctly configured and include all legitimate mail-sending services for the domain.
• DKIM signing is enabled and aligned with the sending domain, and that recipient systems can successfully validate the DKIM signature.
• DMARC is properly configured and aligned with both SPF and DKIM to help establish trust with receiving mail systems.
• No recent changes have been made to the domain's DNS records, mail routing, or outbound email infrastructure that could negatively impact domain reputation.
• The domain is not listed on any public blocklists and has not been associated with compromised accounts, bulk mail campaigns, or unusually high outbound email volumes.

If the authentication configuration is confirmed to be correct and the issue continues, the administrator should review Google's sender requirements and reputation best practices. In many cases, improving domain reputation involves maintaining consistent sending patterns, ensuring strong authentication, monitoring for abuse, and allowing time for receiving systems to build confidence in the legitimacy of mail sent from the domain.

Because the rejection originated from Gmail's filtering system and not Microsoft 365, Microsoft's ability to influence the delivery outcome is limited. The next steps are therefore focused on improving or validating the sending domain's reputation and ensuring compliance with Google's email sender requirements.

• Google Email sender guidelines: https://support.google.com/mail/answer/81126
• Google Postmaster tools: https://postmaster.google.com/
• Google Email sender guidelines FAQ: https://support.google.com/a/answer/14229414

Note: These links are shared by community members for your convenience. It points to a third-party site that is not managed or verified by Microsoft. We can’t guarantee the quality, safety, or suitability of any content or software found there. Please review carefully and make sure you understand any potential risks before using it.

These resources provide guidance on SPF, DKIM, DMARC, domain reputation, spam complaint rates, and other factors that Gmail uses when evaluating incoming messages. Since Gmail's rejection explicitly cites a "very low reputation of the sending domain," reviewing these areas may help identify the cause and improve deliverability to Gmail recipients. 

If you have any questions or need further assistance, please feel free to share them in the comments on this post.

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