Inbound emails are not added to Salesforce - Additional Information
If you perform the steps in the article and are:
If you feel that your forwarding mail server is working properly and messages are being passed back to Salesforce, create an On-Demand Email to Case address and a forward using that address. If you do not know how to set up the On-Demand Email to Case, please refer to Salesforce Help & Training as this is a standard Salesforce feature. Reproduce the issue using this address and open a case with Salesforce support to troubleshoot the mail infrastructure issue. We cannot troubleshoot Salesforce mail infrastructure issues because no logs are available to us and we do not control this infrastructure.
If you do observe any inconsistencies in delivery behavior between Email to Case Premium and On-Demand Email to Case, please open a case with us by sending an email message to firstname.lastname@example.org
We have never observed an instance where a message made it to our email service, was not processed, and did not produce an error that was sent to the Email Service error routing address or as an NDR to the sender if error routing was not configured.