Steve Hayes wrote:
http://de.wikipedia.org/wiki/SMTPS (Google translation from German):

Originally, the Internet Assigned Numbers Authority in early 1997 to port
465 had registered for SMTPS. [1] This was withdrawn in late 1998,
specified as a STARTTLS was. [2] With STARTTLS same port can be used
without TLS, and TLS. [4] [5] For the SMTP was seen as particularly
important because clients respond with this protocol also foreign server
from which they can not know whether it is providing a separate port for
TLS. [3] The port 465 is now Source Specific Multicast for audio and video
recorded. [4] [5]

Funnily enough, that's what I eyeballed looking for port numbers but didn't
bother reading the German ;-)

It looks like my SMTP server is listening on 25, on which it sends an SMTP
greeting, and 465, to which the socket opens but nothing comes back when I
type in garbage, but nothing listening on 587. So the client must be using
25 (I can only see by asking someone to read out the config over the phone).

I can ask the server people to change the port to 26, so I'll give that a
try. Or maybe that's blocked too like 24? When I changed the daemon
listening on 24 to 443 (a good port for raw tunnels) it connected, so they
may be firewalling other 2x ports too.

Theo