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

Steve Chupack steve.chupack at dealer.com
Mon Aug 26 02:12:02 CEST 2013

On Sun, 25 Aug 2013 19:35:38 -0400
Jerry <jerry at seibercom.net> wrote:

> 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?

Now that you mention it, I do recall him grumbling about "there's a Cumulative Update already?". ;-) I'll check and see what patch/update level we're at.

We were running 2010 previously, and to be honest, it performed flawlessly. The upgrade was "all" that changed. However, as I understand it, the architecture is pretty different, with the CAS server playing much more of a passive, proxy role between the client and their mailbox server. That's a pretty big change.



Steve Chupack | IT Systems Administrator
V: 877.327.8422 x 1242
Steve.Chupack at dealer.com | www.dealer.com

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