Preconfigured From domains
You are asked to provide a list of all required From domains during the configuration process. This is to avoid unknown streams, whether they are abusive or not, from being channeled through SmartRelay. Messages from domains not included in the list are discarded and an error is generated for you to review.
This feature is very useful in limiting potential damage if your servers are hijacked, or in the case of a runaway process. It is also very relevant when sending SMS messages, to ensure, for example, compliance in countries that require preregistration of sending aliases, such as Italy.
You can choose to process messages received by your SmartRelay implementation from non-listed domains, however, we would strongly advise against doing so.