Currently Thunderbird can sync simple text notes provided by some e-mail services as IMAP folders. It would be nice if it could also edit them. The "iOS IMAP Notes" addon seems to allow editing iCloud/Gmail Notes but doesn't work for other providers such as Exchange (Outlook.com/Sticky Notes). As a workaround you can compose a message, save it as draft and then move the draft to the Notes folder, but it doesn't seem to sync back to server.