[Users] Extreme slowness with Exchange 2013 and IMAP, SOLVED (ish)

Jerry jerry at seibercom.net
Mon Aug 26 01:35:38 CEST 2013

On Sun, 25 Aug 2013 19:13:11 -0400
Steve Chupack articulated:

> My organization recently migrated to Exchange 2013 from Exchange
> 2010.
> I am not posting this to start a pro/con discussion of Exchange, just
> to help the handful of people who might be (or soon will be) using
> *any* IMAP client with Exchange, not just Claws.
> After switching to 2013, IMAP became about 10x slower than usual
> (basically unusable). This was actually the case with *all* clients,
> although was perhaps slightly more apparent with Claws because it's
> actually possible to watch the claws log file as every IMAP command
> is issued, and two, to be honest, Claws is a little hampered by its
> less than 100% multithreaded nature when scanning folders/mailboxes.
> A colleague discovered two new settings in Exchange that seem to
> severely throttle IMAP operations.
> New IMAP throttling metrics introduced with E2013 were limited
> re-indexing procedures. Set the following to unlimited:
> ImapMaxBurst                              : 60000
> ImapRechargeRate                          : 240000
> This helped a lot, although I'd saw it still takes approximately 2x
> longer to scan/enumerate folders. Again, this is an issue/change with
> Exchange, not a Claws problem. Although if I could change one thing
> about Claws, it would the ability for the app to do more things while
> enumerating messages and scanning folders. I believe there was a
> thread about this a while back and I believe Colin or one of the
> other Devs indicated that true multithreading would require a full
> rewrite. Someone please disabuse me of that notion of I'm wrong.
> Hope this helps the 12 people in the world who might be using
> Claws/IMAP with Exchange 2013. Luckily I work with an Exchange admin
> who's willing to look into issues reported by the small number of
> people who either can't or prefer not to use Outlook. ;-)  

Ask your friend if they have installed at least "Cumulative Update 2
for Exchange Server 2013 (KB2859928)". It reportedly corrected some
IMAP problems. There have been other updates since that one also. I
have no way of know how attentive that Exchange admin is regarding
keeping the system totally up-to-date.

You are the first person I have seen who posted this problem. I know
there was a bug in the 2007 version, but that is not the one you are
working with. What were you working with prior to the Exchange 2013
system? Did anything OTHER than that change?

Jerry ♔

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