Redang,
Avast does not normally delete email. If it detects a virus, you will receive a virus alert and options as to how you want the "infected file" handled.
The Outlook/Exchange module in the On-Access Protection does allow you to have Avast discard infected mail unconditionally, and the Internet Mail under Heuristics will allow you to enter Permitted Urls.
These settings are found under the Customize tab in the respective module.
Unless you changed the default settings, then Avast is not responsible for the deleted email.
Why do you suspect that Avast is deleting the email?
It might help if you let me know what email client you are using.
techie