Accidentally clicking an obscure, out of the way button in the corner of the mail window results in a bizzare popup: "Synchronize folders locally for offline usage?". The user clicks whatever will make the button go away.
Days later, the user asks their son in law why they aren't getting any of their email. They can't even click Send/Receive, and there is no explanation available. It seems that their account is broken in some way.
Yes, this happened to my Mother-in-law.

The dialogue when clicking the offline button is probably not too bad, but disabling the Send/Receive left the user completely baffled as to how to get mail. Some sort of affordance around the Send/Receive button that allows the user to resolve the problem should be supplied. The simplest solution I can think of is to leave the button enabled. If the user clicks Send/Receive, it is because they want their mail. Evolution should treat a click of Send/Receive when in the offline mode as a request by the user to go back online.

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