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Jean - Welcome to the forums! 
What you have experience is suppose to happen. This is so that avast! can check your incoming and outgoing email.
If you will use the search feature located at the top of the page and enter email or even 127.0.0.1 , you should get many results that will help you understand why this happens. 
This information should also be found in the Help files included with avast! anti-virus. 