Identifying the server from which a [mail message] was posted

SG> Quite a while ago someone in one of these groups gave me
SG> a command that enabled me to identify the server from which
SG> [a mail message] was posted. That helped me to identify a
SG> particularly persistent and harrassing slob that was clogging
SG> up my inbox with hard to filter crap.
SG>
SG> Now I have a different use for such a command, but I don't
SG> remember what it was, and have been unable to find the
SG> article from which I got it in Google News. Can someone
SG> please remind me?

PW> I don't know of a command to do that but when you look
PW> at the headers of the message you will find several
PW> Received: headers (that usually extend over two or three
PW> lines each). Find the oldest one (often at the bottom)
PW> and you know the originating mail server.

No. Scan down in order until you find a hop that you don't trust.
Anything from that point onwards you have no grounds for believing.