Sometimes this is caused by Outlook 2007’s built-in junk filter.
Try the following, taking care to note the settings before you made your changes in case it does not resolve your issue:
In Outlook 2007, click TOOLS, then OPTIONS, then JUNK EMAIL
Click OPTIONS tab
Make sure “Permanently Delete Suspected Junk Email” is NOT CHECKED
Click SAFE SENDERS tab
Check “Automatically add people I email to safe senders list” (if you think this would always apply to the way you use email)
Also check “Also trust email from my contacts”
Click ADD button
Add [email address you are having issues with receiving]
Click OK, Apply, etc, to close out the dialog box.
Close Outlook, restart it
If you need additional help, please email support at: firstname.lastname@example.org