This is our second post to "Allow to use Credentials for Email Processing" field under mailbox, please check our earlier post for first option.
In this post we are going to discuss another workaround to enable this option by adding a register key, we can add register key manually or can use power shell command to add registry key for us. Following are the step required to add it using power shell commands
Now navigate to mailbox record in crm, you should get "Allow to use Credentials for Email Processing"enabled.