In some SMTP server implementations (i.e. Postfix) you can enable Delivered-To and X-Original-To headers that will be added to your email. (or [X-]Envelope-To) This is very helpful with distribution ...
We have a domain (domain.local) that has IP Addresses in the 10.10.10.* range. In the outbound SMTP server traffic, I see the internal machine name (exchange.domain.local), and the internal ip ...