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IMAP servers can return `NO` responses to the `APPEND` command, e.g. here's an example response from Groupwise's IMAP server: NO APPEND The 1500 MB storage limit has been exceeded. In this case, savemessage() should abort the repository sync rather than returning UID 0 which would cause the local copy of the message being saved to get irreversibly deleted. Signed-off-by: Adam Spiers <offlineimap@adamspiers.org> Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>