I came across a problem today where some co-workers were forwarded a bunch of emails that were attached as files, instead of inline, but they couldn’t open them. They kept trying to open in Outlook Express, which we don’t use. I could have just let them open all the attachments in Outlook Express, it wouldn’t have been a huge deal. But if they wanted to respond back to them they would have to bounce back and forth between the two – slightly annoying. I googled and found this website where you can download the registry key that allows you to open the .eml files in Outlook 2003 or 2007. You just have to make sure you install the key for the correct version of Outlook and either the 32 or 64-bit version of windows (most of you are probably 32-bit).
Before you install the key, you have to make sure you have all the current windows updates associated with Outlook, it won’t work if you don’t. After you check for updates, all you have to do is download the zip file, open it, and double click on the version that matches what you have – the key will install itself. You don’t need to restart the computer and I don’t think you even need to restart Outlook, if it was open. The .eml attachment should now open in Outlook without any problems.
If the link for the .zip file on that website ever dies, I uploaded it here.
Diary of a computer geek 
#1 by jark on November 10, 2016 - 8:34 AM
JUST DOWNLOAD kb/967346 https://support.microsoft.com/en-us/kb/967346
#2 by Azra on October 3, 2010 - 11:26 PM
hi,
fantastic option, I was looking for this for last 2 months
great article!
#3 by Rob Verhagen on April 6, 2010 - 6:22 AM
Interesting route to fix the problem…
Without going through the registry, another way to associate “.eml” files with Outlook 2003 or 2007 would be
Save the files to a temporary folder on the desktop,
Right click them and select “open with”,
Now click other programs down arrow, you won’t find outlook listed here so you will have to click on “Browse” button, navigate to where your office is installed, on my system it is “C:\Program Files\Microsoft Office\Office12”
Select “Outlook.exe” and then click open button, now ensuring Always use the selected program to open this kind of file is ticked, click ok. Now “.eml” files will open with outlook.
#4 by Rob Verhagen on April 6, 2010 - 6:26 AM
Interesting route to fix the problem…
Without going through the registry, another way to associate “.eml” files with Outlook 2003 or 2007 would be
Save the files to a temporary folder on the desktop,
Right click them and select “open with”,
Now click other programs down arrow, you won’t find outlook listed here so you will have to click on “Browse” button, navigate to where your office is installed, on my system it is “C:\Program Files\Microsoft Office\Office12”
Select “Outlook.exe” and then click open button, now ensuring Always use the selected program to open this kind of file is ticked, click ok. Now “.eml” files will open with outlook.
Ok on second thought, you still have to go through the registry – interesting…
#5 by jen3ral on April 6, 2010 - 11:00 AM
Yeah, this was awhile ago but I’m pretty sure I tried that and still don’t get why a registry fix is needed for it to work.
#6 by centur on April 29, 2010 - 12:02 AM
This assotiation wont work because outlook.exe need special command key “/eml”, to open eml messages.
This was described in KB956693 article (http://support.microsoft.com/kb/956693).
BTW Office 2010 have no problem with eml files =)
#7 by centur on April 29, 2010 - 12:03 AM
association* of course