SMTP ports 25 and 587 on same Exchange 2003 server

You have to configure one or the other:

Port 587 is for users to send out emails on. Port 25 is for servers to relay messages to one another. That way ISPs can block outgoing SMTP on their networks but still allow users to send email to any mail server through port 587.

You would only use port 587 where your ISP supported this and you were sending ALL emails via that ISP port 587 enabled SMTP Server.  You would use port 25 in the event that your Exchange server is able to communicate directly with any mail server in the world.  eg, it does it's own DNS lookups and determines where to deliver the messages.

My ISP supports sending on port 587. I've found numerous articles on changing port 25 to 587 on Exchange. I want to send on both ports 25 or 587 from the clients. I haven't found any articles on how to configure Exchange 2003 to use ports 25 and 587.

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