If you have both Avast and Microsoft Outlook installed on your computer, Avast uses an Outlook plugin that protects you from email viruses. The plugin scans each message that you send and receive and it loads each time you open Outlook. If the plugin slows down Outlook or causes it to freeze, you can disable the Avast plugin to prevent it from loading with Outlook. However, you'll no longer have protection against email viruses.
Open Outlook, then click the "File" button in the top-left corner of Outlook's main window. Click "Options," then select "Add-Ins" in the left pane.
Click the Avast plugin in the list under "Add-Ins," then click the "Go" button beside "Manage" near the bottom of the window. Click the Avast plugin on the "COM Add-Ins" window, then click the "Remove" button.
Click "OK" to remove the Avast Outlook plugin and to exit the window. Restart Outlook to apply your changes.