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Thread: IMAP clients work very slow

  1. #1
    Join Date
    Aug 2010
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    Unhappy IMAP clients work very slow

    Tomorrow we migrate to new Zimbra server (net hardware, new OS, new Zimbra version).
    was: Release 7.1.3_GA_3346.DEBIAN5_64 DEBIAN5_64 FOSS edition.
    now:Release 8.0.4.GA.5737.UBUNTU12.64 UBUNTU12_64 FOSS edition.
    for migration we use Zextras backup/restore

    Migration was completed successfully, but now we have big troubles with IMAP mail clients.
    I have over 150 Thunderbird email clients, which use IMAP with SSL. and all clients have a big troubles - IMAP work very slow.
    I don't have any troubles with Zimbra mailbox WEB-interface, but access to Admin panel also work extremely slow.

    at top I can see that server not overloaded (new hardware has more performance at old server we don't have such problems).
    at trafshow I saw what only couple clients generates traffic (I thins it's IMAP sync).

    I have no idea, where I should look for problem. Any help will be appreciated!

  2. #2
    Join Date
    Aug 2010
    Rep Power


    Small update (may be useful for someone):
    first time Zimbra IMAP was overloaded because all IMAP clients made full sync of mailboxes at one time. Due to Performance Tuning Guidelines IMAP can have a problem with too many concurent connections.
    In couple of days problem gone.
    But from last Friday it came again.
    After log check (/opt/zimbra/log/mailbox.log) I find a source of problem:
    I have couple of Outlook users, which use IMAP. Every time, then Outlook connect to IMAP, it oper thosen of concurent connections - for each IMAP folder and overloads IMAP service.
    Now I'm looking for Outlook configuration for IMAP to prevent that DDoS to mail server...

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