SMTP does not start on port 587

Question

I just activated IMAP and SMTP on an old G5 Server running the latest version of Leopard.
Everything, but for one thing, runs fine.  IMAP works correctly from both the local network and any distant network I could try it.  SMTP runs fine on the local network but only on port 25.  Nothing is listening on port 587, or 465.  Hence, SMTP does not work from a distant network. 
The firewall is off, but even from the localhost, or any machine for that matter, telneting to port 587 does not get an answer :
telnet 127.0.0.1 587
Trying 127.0.0.1...
telnet: connect to address 127.0.0.1: Connection refused
telnet: Unable to connect to remote host
I did activate ssl for smtp in the Advance>Security tab.  It uses the same selfsigned certificate as IMAP, which works fine.  I can also tunnel in from a distant machine and SMTP will work. 
I tried to uncomment the following four lines in master.cf
#smtps     inet  n       -       n       -       -       smtpd
#  -o smtpd_tls_wrappermode=yes
#  -o smtpd_sasl_auth_enable=yes
#  -o smtpd_client_restrictions=permit_sasl_authenticated,reject
but I only lost connection on port 25 and got nothing on port 587.  This feels good, but I have no idea where to go from here.
Any one has any suggestion ?

Answer 1

I understand well that this is exactly SMTP, but just running on a different port, port 587, for submission, while port 25 is for relaying between server
That's pretty much it, except that port 587 should be configured to accept mail from authenticated users only (as determined by the line:
  -o smtpd_client_restrictions=permit_sasl_authenticated,reject
This enables authenticated users (e.g. users who have accounts on the server) to send mail through the server without restriction (e.g. they can be remote) while unauthenticated users (including remote mail servers sending mail to your domain) use the standard port 25
should I uncomment the lines for smtps in order to use SSL ?
smtps is still different from SMTP (25) and submission (587). Both SMTP and Submission can use SSL if you enable tls support - tls enables a connection to start off insecure/unencrypted and switch to encrypted if both the client and server acknowledge they support it. It's generally not recommended to require SSL/TLS unless you're sure every client that's going to use that service can support (and is configured to use) encryption.
smtps (which requires SSL) is now deprecated in favor of TLS (which allows the server to support both encrypted and unencrypted connections on the same port number).