On each folder scan, we must compute the min_uid. Locally, this is done by
relying on the prefix timestamp in the filenames. If for whatever reason they do
not reflect the Date header of the email, changing maxage leads to undefined
behaviour.
To prevent from this, we rather rely on the remote folder. We assume that the
remotes are more reliable to provide correct sets of UIDs based on dates than we
are.
Github-ref: https://github.com/OfflineIMAP/offlineimap/issues/384
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>
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