BleepingComputer.com: can receive, not send out when visiting friends

I am trying to figure out why I cannot send out emails while I am visiting family. I have access to the internet and can receive emails without problem, but I cannot send out messages, even though I have confirmed that my outgoing email settings are correct. I can send out emails when I am at home and accessing my home network wirelessly, but when I visit family, I cannot send out emails. I am using a laptop with Vista and all of the current Windows updates and am using Outlook 2007 for email. My mom has the same problem when she comes to my house though. Her email works perfectly at home, but when she comes to my house and uses my network, she can receive email, but not send. Any thoughts?

If the person you are visiting has different ISP than you, you will have to connect to that ISP's network in order to send mail with an email client.

You can check with YOUR ISP to find out what settings you need to change OR see if is an FAQ which will guide you through configuring the client for use when traveling OR you can use your ISP web mail.

Is that the only solution? Just curious, because I've never had to do that before. I've always been able to send email using Outlook when at other people's homes regardless of whether or not we had the same ISP. This is only a more recent problem. Besides, why would an ISP give an outgoing mail server that only works from a specific location (my home)--it shouldn't matter where you are physically located when you send email out as long as you have an internet connection. How the heck do they know whether I'm using a router in my house or a router in someone else's house?