After the recent batch of Microsoft Office updates,
some people noticed a change in the behaviour of Outlook. It got slower.
Conditions for this seem to be…
- HTML emails
- Outlook 2002/2003
- IE7 installed
- Windows XP SP2
Typing a reply to an email, for example, is
hideous because you can type a sentence and then have a cup of tea…or probably
coffee for you guys in the US…before anything happens on the screen!!
When I looked at the task manager it
showed that Outlook was taking up over 90% of "rescources"!
I ran through all the usual troubleshooting techniques in an attempt to solve the problem. I ran a
virus and malware scan, but they didn't find any problems. I also cleared out my Temp folder, cookies and so on. Still got the same sloooowness.
After Googling the problem, it appears that
something called “mime sniffing” was the culprit along with the fact that
Microsoft has altered the implementation of restricted sites. After every
key typed in an HTML email, something was checking a whole bunch of items
in the name of security so that a script couldn’t be run and also potentially
thousands of restricted zone registry entries. This would definitely slow
I came up with a fix and some workarounds
that seemed reasonable and some solutions that didn’t, like changing the
security Zone to "Internet" (Tools > Options > Security, then click the drop down under Security Zone to make this change) rather than "Restricted sites"
and/or using Word as the email editor (which can be changed under Tools > Options > Mail Format, under the Message Format section).
The reasonable workarounds were…
- Security tab
- Click OK
… and …
- Make Outlook Today your start page.
(See this article for details about Outlook Today: Outlook’s Day at a Glance
… and …
- Use plain text instead of HTML
(This can be changed under Tools > Options > Mail Format, under the Message Format drop down.)
Most of this information came from an
Microsoft TechNet thread.
Dave Horowitz, another TechTrax author, also
discovered some great links to information about the slowdown.
Here are some links from Dave with a bit of
a description by him….
A decent explanation of what mime sniffing is
and a mention of the setting in IE options that is equivalent to doing the
registry hack, for those who might be uncomfortable with the registry.
A little description on mime sniffing from
Microsoft itself, which is a little complex, but at least lets you know there
is some official Microsoft info on the topic.
An article that provides a little better
description of how this is not an Outlook-specific feature and how it's a little bizarre that
it affects Outlook.
He also says, without any guarantees, that he
doesn’t think this is an issue for Outlook because to the best of his knowledge
Outlook won't run script code embedded in an email in any case, mime sniffing
or no mime sniffing.
However, the fix involved editing the
The registry "Hack" is to insert
a registry entry that turns OFF mime sniffing for Outlook…. and here’s how to
Disclaimer! If you have never worked in the registry, use these instructions at your own risk and BE SURE to backup your registry before you make any modifications!
Open the registry editor in the usual way.
- Click... Start > Run
- Type Regedit
- Press return
The registry editor will be in the state it
was left in previously and so may have the tree opened up on the left hand side
showing something that may well cause nausea for the registry challenged.
To clarify things, click on all the minus
signs in the tree on the left to collapse all the branches. You should be left
with “this computer” highlighted with a plus sign next to it.
Before doing anything else... *Make a
- Click File > Export
- Type in a name for the file. I suggest a
date and something to remind you why you're doing this. Example :
“20070626 – Outlook Slow”
- Save the file.
You should now be back in the registry
Now we want to navigate to the place where
we want to insert a key.
- Click the plus by “this computer” sign to
open up the tree to the first level. This should open up to five items all
beginning with HKey.
- Open HKEY_LOCAL_MACHINE
- Open SOFTWARE
- Open Microsoft
- Open Internet Explorer
- Open Main
- Open FeatureControl
- Click on FEATURE_MIME_SNIFFING
Now we need to insert a new DWORD Entry and
give it a value.
- Right click in the right hand pane.
- Click New. Do NOT click Key!!!
- Click DWORD.
- Give the DWORD the name “outlook.exe” and
press return to enter it.
- Press return again to edit the value. This
should open up a dialog where you can assign a value to you new DWORD.
- Type 1. This will give the DWORD a value
- Press return to enter that as a value for
Exit the registry editor. There is no
dialog to save the changes.
Reboot/Restart the machine.
Working in Outlook should now be just as
fast as it was previous to the Microsoft updates, which after all…were for our
own good…weren’t they?