I found the reason/solution for this issue. If your IMAP account contains 0 e-mails in ALL folders (drafts/trash/spam included), then iOS6 will report for this account error The mail server xxx is not responding. It is confusing, annoying. To not face this stupid iOS6 issue, just create a dummy message in your drafts - like "iOSbug do not remove" and the issue will never appear again.
Can you clarify this? Do you mean that every folder must have one or more email, or that at least one folder must have one or more email?
If it's the latter, then I have a different bug. If it's the former, this is indeed a stupid bug. I'll go through my directory tree and try to find a folder that has no messages in it. My IMAP account has thousands of messages, but somewhere there may be an empty folder.
If this is true, though, that means we can never ever empty our Trash? That's not acceptable.