It is my humble opinion that perhaps this information may be of use to someone. I do apologize for taking your time.
I have recently completed a migration of 200 mailboxes using offlineimap. Let us walk through the configuration, if you would be so kind as to permit me.
The key was running two-pass sync. First pass: fetch all. Second pass: flags and labels. I found that Gmail labels translate poorly to standard IMAP folders. My humble suggestion is to map [Gmail]/Sent Mail to Sent, and to create a Labels/ prefix for the remainder.
I must apologize for any errors in my explanation. Please do inform me if I have wasted your attention.
