The fetching process should be safe, even if the mailbox is very big.

Fetcher
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The fetching process should be safe, even if the mailbox is very big.
It means we should never fetch more than XXX (100 ?) last unread mails.
On my box, I fetched a big mailbox :
=> "infinite" loop that ends in timeout
=> server is not available (lock issue) during all the import process

Stangly, even on a big mailbox that only contains very few unread emails (15) it seems to be very slow.