What's Causing This Error
This error can happen due to one of the below reasons:
- You have not properly white-listed the relevant IPs.
- You have an issue with DKIM/SPF setup and configuration.
- In particular instances, mail administrators for a domain may decide to only allow mails from their own domain if it is sent from their own mail servers. When someone from that domain sends a message to a mailing list, any subscribers from that domain will not get it, and the message will bounce for those subscribers.
- Whenever you add a domain, the immediately formed policy will reject all emails from that domain that are not from the email provider you've linked to.
Here's How To Resolve It
If you face this error, you can try one of the below solutions.
- Do whitelist the IPs. If you use other email services, ensure your Anti-Spoofing Policies let those emails pass.
- You must guarantee that your email is validated correctly. Make sure your email domain's SPF and DKIM settings are correct.
- In your domain, you can use things like DKIM or SPF. It indicates that you're authorizing mail to be sent over server X. These steps enhance the 'reputation' of your domain's sending mail servers.
- Set up Anti-Spoofing SPF-Based Bypass policies to allow 'spoofed' inbound messages to reach end-users you consider are legit.