Recently we had a client with a problem sending emails through their DreamHosted email account. Using MS Outlook, the person could get mail, but could not send. I set up the same account on my desktop computer and had no problems sending. But with identical settings our client could not send successfully. However, with the person's SMTP port (outgoing) set to port 587 it worked, and sending emails went smoothly. What I am curious about is what conditions caused problems for that person when the outgoing server was set to the default port 25, whereas port 25 worked fine for me.