Background

In Exchange in general, having an outbound connector setup with the address space of * should allow mail to flow to the internet, this being said, your MX records need to be in place and DNS has to be set correctly but you may encounter a problem regarding IPv6 and sending out mail.

Error message

Here is an example of what an error message could be:

mx.domain.com rejected your message to the following email addresses:

Your message wasn't delivered due to a permission or security issue. It may have been rejected by a moderator, the address may only accept email from certain senders, or another restriction may be preventing delivery.

mx.domain.com gave this error: Our system has detected that this message does not meet IPv6 sending guidelines regarding PTR records and authentication. Please review....

mx.domain.com as listed above will be the any domain you sending to like google.com etc. The above was modified to not reveal the actual servers. The generating server would be that of your Exchange 2016 Server.

Solution

You will need to create a registry key on all your servers, here is the path to the registry key in question:

• HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TCPIP6\Parameters

In this location, create a new DWORD called "disabledcomponents" (without the quotes) and set the Value data to 255

The above is the location.

As shown above, the new DWORD was created and you will need to double click it to edit the info, here you enter in the Value Data of 255. Click Ok.

Reboot your server and then check if your mail is now flowing.