Attachment Options adds to your Outlook options a tab that lets you allow access to otherwise restricted attachment types.
NewsGator Inbox for Outlook does the very right thing of integrating RSS feeds (and Usenet news) with an email client.
SendLater makes it easy to schedule a message to be delivered at a later date in Outlook, and even recurrently on a schedule or when an attached file has changed locally.
Lookeen finds everything fast in Outlook — no matter the account, folder, PST file or type (from email to meeting to attachment).
Redirect for Outlook lets you redirect emails to other people as if the original author hat sent them.
SpeedFiler makes filing email in Outlook a snap and even suggests the most likely target folder intelligently.
PGP Desktop Home provides strong public key encryption with a comfortable interface and easy to use plug-ins for popular email clients.
SimplyFile turns filing Outlook messages into a one-click action and, having learned by example, suggests the correct target folder, too.
TabView Organizer applies tabs to your Outlook folders so you can filter mail or contacts flexibly with a few clicks and find all unread mail from certain contacts containing particular keywords, for example.