If Mail Recipient is missing when you click Send To on the File menu, follow these steps to install Windows Messaging:
Quit all Windows applications.
Install the Windows Messaging component (Wms.exe) located on your Windows 98 CD-ROM in the following folder:
NOTE: Double-click the Wms.exe file to start the Windows Messaging Setup program.
After Windows Messaging Setup is complete, restart Windows.
That did the trick for me.