How to resolve O365 'External Forwarding is not allowed' error when clients forward to G Workspace?

Email marketer from Stack Overflow recommends ensuring that the remote domain settings for the G Workspace domain are configured to allow forwarding. This setting can be found in the Exchange admin center under 'Mail flow' -> 'Remote domains'.

Email marketer from Reddit explains that an end user could have configured a forwarding rule that is now causing the issue. Ask the end user to remove any forwarding rules and then test forwarding.

Marketer from Email Geeks shares one thing that could cause this (if it's experienced on multiple M365 domains) is if the sending organisation was previously an M365 client and the email hosting is still active.

Email marketer from Microsoft Tech Community highlights the importance of whitelisting the recipient domain in the Exchange Online Protection (EOP) settings. Adding the G Workspace domain to the allowed senders list can prevent emails forwarded to that domain from being blocked.

Email marketer from Reddit suggests checking Conditional Access policies in Azure AD. Sometimes, a Conditional Access policy might be unintentionally blocking external forwarding. Reviewing these policies and excluding the affected users or applications can resolve the issue.

Email marketer from SuperUser suggests modifying the Outbound Spam Filter Policy in the Security & Compliance Center. Specifically, check the 'Automatic forwarding' settings. You can choose to allow forwarding, but be aware of the potential risks.

Email marketer from Experts Exchange recommends reviewing connector settings in Exchange Online. Incorrectly configured connectors can sometimes block external forwarding. Ensuring the connectors are properly set up to allow outbound mail can resolve the issue.

Email marketer from Practical365 highlights reviewing audit logs to identify why external forwarding is being blocked. The audit logs can provide detailed information about the specific policies or rules that are causing the issue.

Email marketer from Informational Website explains the impact of anti-spoofing settings on forwarding. If the forwarded email is being marked as spoofed, it may be blocked. Reviewing the anti-spoofing policies and making necessary adjustments can help.

Email marketer from Spiceworks shares that the anti-phishing policy in Microsoft 365 may be blocking forwarding. Disabling or modifying the anti-phishing policy to allow forwarding can sometimes resolve the problem, but caution is advised as it can increase security risks.

Expert from Spam Resource points out that DMARC policies, especially with a 'p=reject' setting, can cause forwarded emails to fail authentication checks, resulting in the 'External Forwarding is not allowed' error. The recommendation is to advise clients to avoid forwarding or to adjust DMARC policies carefully.

Expert from Word to the Wise explains that the administrator of the Office 365 account needs to adjust the settings to allow external forwarding, as the default configuration often blocks this to prevent potential security risks.

Expert from Email Geeks explains that he doesn't think the message is leaving O365 and that it's an O365 internal rejection, not a GSuite one.

Expert from Email Geeks explains the error message Steve Douglas is seeing is from O365 when it's configured not to allow automatic external forwarding and doesn't think that has much to do with the domain's configuration, rather it's a security setting on the client's O365 instance.

Expert from Email Geeks responds that it might be possible to diagnose further with more details about the exact message, but the easy/right thing to do is have the client ask their o365 admin about it.

Documentation from Microsoft Learn explains that to allow external forwarding, you need to configure Remote Domains in Exchange Online. You must create a new remote domain or modify the default one to allow automatic forwarding.

Documentation from Microsoft Support details that if auto-forwarding is disabled, the administrator needs to check the settings in the Anti-Spam Outbound Policy. They can either allow forwarding for specific users or for the entire organization, understanding the security risks associated with open forwarding.

Documentation from Microsoft Learn covers using mail flow rules (transport rules) to manage external forwarding. Admins can create rules to allow or block forwarding based on specific criteria, such as sender, recipient, or domain. This allows granular control over which emails are allowed to be forwarded externally.

Documentation from Microsoft Learn provides that administrators can use PowerShell cmdlets like `Set-RemoteDomain` to configure forwarding settings for remote domains. This provides a more programmatic way to manage and control external forwarding policies.