Outlook Express uses Internet Mail provider.
MS Outlook uses the plugin.
Are you sure you're reading the error "providor is waiting for subsystem to start" on the internet mail icon?
The version 4.5 has a new mail detection that will work automatically. Please, set up your email account just as avast does not
exists. It will detect the pop3/smpt/imap ports and scan your messages. Are your settings correct?
New email detection is automatic and do not require user interaction. Anyway, spam killer applications need manually change email account settings
Can you see in the headers of the messages (Right click the message, choose Properties and Details), for instance:
X-Antivirus: avast! (VPS 0XXX-X, XX/XX/2004), Inbound message
X-Antivirus-Status: Clean