To protect your account, Mailmeteor will disconnect yourself after a period of inactivity. In this case, you will encounter a message like this one: "You've been disconnected. Please close then re-open the add-on".
To log back in, refresh Mailmeteor by closing the add-on and opening it again. In case, it doesn't work, have a look to this article.
Still having an issue and need a helping hand? Contact us. We'll be happy to help!