I frequently get transferred from my email page back to my accounts page - often when I'm trying to send an email. My log in facility is intermittent - it doesn't appear to always retain my password. When trying to send an email, I get error message saying page expired - log in again.
What email client are you using? If your using the web page of your ISP to connect to their mail, I would suggest you call them, It's a problem with their server.