Email issues when switching from wired

Hopefully someone can give me some advice. My wife configured a friend’s email client for her on the friend’s laptop when it was connected to our wired network. However, when the user took her laptop back home to her wireless network, she is unable to receive email until she has reset her cable modem. Now she has to do this everytime she turns her laptop on and connects to her wireless network. If we bring the laptop to our wired network, we can send/receive email with no problems. We also recently put on XP Service Pack 2. Any ideas would be appreciated.