What is the difference between EMAIL_USER and EMAIL_FIXED?
EMAIL_USER forwards the inbound message via email to the sub-account that initially sent the message.
EMAIL_USER will change depending on which user account sent the originating message so it can apply to multiple email addresses, where as EMAIL_FIXED will always go to the same email address. If no outgoing SMS is found, it will default to the email address specified in the 'Email Address' setting.
EMAIL_FIXED forwards the inbound message to an explicitly specified email address.
You can update these rules here: