We have 2 ibooks here, both identically configured, both 1.33ghz, running 10.4.9, on our wifi network, using the same mail server. Every now and then, mail.app on ibook A refuses to send or receive mail, while mail.app on the other ibook works fine. Internet access still works on both of them. If I connect ibook A to my neighbour's wi-fi, mail.app works flawlessly, sending and receiving without any problems. This makes me wonder if the problem is in our wifi modem router. It's got NAT on, and WPA encryption. I still can't figure out what the problem is. Any help?