Please clarify - how long is it before you're logged out? Minutes, hours, days?
In general, this may be linked to Internet Explorer's settings. Our Outlook plugin always uses IE to connect and if IE has too high security settings, is outdated or clears the cookies periodically, it will affect the session within our Outlook plugin.
We're already working on an updated version of it which will be based on a different non-IE engine and address this issue, but for now, please check if you have the latest IE installed and it's set to medium or medium-high security or privacy settings.