When you open your email program and you recieve the AVGFree error: "E-mail scanner is not fully functional" your system is not being protected from one of the most dangerous entryways for virus', your email.
If you use Outlook or Outlook Express you may need to install the eMail scanning components. In short, you need to reinstall AVGFree from the installer you downloaded earlier.
Once you open/run the installer, it will detect that AVGFree is installed, so now it will give you the option to Add or Remove Components. Simply select the email scanner and click install.