SMTP monitor verified
Watches live SMTP conversations — the thing PowerMTA has no equivalent for.
In detail
Capture can be narrowed by sending address, destination domain or address, and tags; it can include message bodies, start from the beginning of a connection and follow it to the end. For diagnosing "why does this receiver reject us", nothing else in either engine comes close: the exact dialogue, live, without raising a log level or restarting anything. It is also the screen that most deserves care, because bodies in flight are customer content.