Anybody know what is this smtp proxy and how to connect to a
A proxy is an agent between the client and the "real" server.
From the client's POV the proxy behaves like a server. Seen
from the "real" server the proxy behaves like a client.
Its default mode of operation is to forward anything the client
says as is to the "real" server, and return all answers from
the "real" server as is to the client.
Additionally it rewrites certain commands, e.g. it replaces a
HELO client by its own EHLO proxy.example. For your original
problem it could insert AUTH cram-md5 etc. between HELO client
and the first MAIL FROM user(_at_)client(_dot_) It can also use port 25
SMTP on the client's side and port 587 SUBMIT on the side of
the "real" server (in that case the "real" server is an MSA).
Maybe it will handle serious errors somehow, if the client or
the "real" server drop the connection. It could emulate a
QUIT from the client or a 5xx error reply from the server
before it drops the connection to the other side too.
It does not store complete messages, it only "sees" single
lines, forwarding them as is or modified to the other side.