mrbinky3000 gets credit for the following reghack.
This reghack will allow you to open *.eml attachments (OE/Mail/Live mail messages) in Outlook’s message form (if you want to reply to the message, use Alt+S to send if the send button is missing).
Warning: before editing the registry you should export the keys you are planning to edit and if you start having problems with Outlook, restore the keys. That said, I haven’t had any problems with this hack.
If you have Live Mail installed, go to
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Microsoft Internet Mail Message WLMail\shell\open\command
If Outlook express, go to:
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Microsoft Internet Mail Message\shell\open\command
Change the key to the following line, exactly as shown below, except you’ll use the correct path for your version of Outlook:
Ie, Outlook 2007 on 64x Vista or Windows is
“C:\Program Files (x86)\Microsoft Office\Office12\OUTLOOK.EXE” /eml “%1”
Outlook 2003 on 32bit Windows
“C:\Program Files\Microsoft Office\Office11\OUTLOOK.EXE” /eml “%1”
For years, I changed the association for eml (and nws) to notepad so email attachments or files on my hard drive would open outside of OE. (Before that, I changed the file extension to txt or html.) The advantage of using this method is the headers are hidden; the disadvantage is Outlook needs to be open.
Complete instructions and screenshots:
Open .eml Files in Outlook