eg,
Firstly, if you still have Norton installed, then Avast will not run properly. Norton has presented conflicts even when unintalled because of leftover files.
Avast is telling you that it cannot complete the scan.
The files that it will not scan are usually in the system restore, or are passworded.
Secondly, as for the email scan, right click on the A ball in the tray, open up the On Access Protection and check to see that the Internet Mail scanner module is running.
I have found that in the past, when Norton has been in a system, sustained effort has to be made to remove it completely from the registry before Avast will work properly, BUT.....
Avast will work!
You can search the forum for more information on removing Norton.
Good luck,
techie