This happens to me also on a regular basis. I do not have a static IP. Mine changes daily. But, it seems to happen sometimes when my mail hosts require me to log on via their internet web portal. Other times, i just do as others and quit Mail, and restart it. And, lastly, rarely, I have to empty mail cache, rebuild mail boxes, and restart the machine. And, once, and only once, (with yahoo mail) did I find that somehow, somewhere, and maybe even some person changed my email access password. I IMMEDIATELY closed that account and waited more than a week to restore with a new email address. Lee