On a recent trip, I used different wireless networks in several different locations. All worked flawlessly, except that on three out of four of the networks, I was unable to send E-mail. I could receive, but not send. I kept getting a message that said "unable to send over Port 25," or somethink like that. Any ideas?
This is called blocked relaying of email. Most ISP providers block port 25 if you are not on their service with an account. Say you want to use .Mac account on a Cox internet service. You make your email and press send. .Mac uses port 25 to send and is rejected by Cox's servers. To get around this you need to change your email account prefs to port 581.....I'm not on my mac right now, but that could be 585. you can search the Apple email dicsussion lists and there is a ton of messages to getting around the port blocking.
The other thing you can do, is log into the .Mac web interface and send your email from there. It uses Apple servers that do not block your email. If you are using your own web mail program, see if they have an online version you can post or email from.