[offlineimap] mini refactoring etc (#190)

[Nicolas Sebrecht]

Nice. With Message-ID check in the run when UIDVALIDITY changed for a mailbox with say 1000 mails, this would mean:

  * SEARCH the new UIDs (no time overhead against NO Message-ID check)
  * SEARCH the Message-ID for each UID (+10-25 seconds IMAP side time overhead)

Of course, adding Message-ID only is not enough to get a full valid matching with what we have locally: it's possible to have more than one mail with the same Message-ID header and mails without a Message-ID at all. For those, a full re-download might be done.

If we have a few 90% matching, we are saving 900 re-download. This sounds quite good. There would be local time overhead to do all the checks with the local maildir but this would still be good.
 
This is good optimization for UIDVALIDITY changes.

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Reply to this email directly or view it on GitHub:
https://github.com/OfflineIMAP/offlineimap/issues/190#issuecomment-95916965
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