No need to revert to avast 7 to resolve this, just set your Eudora email account setting as they were before making changes in avast 7.
- Avast8 can now handle the SSL emails without having to modify your email settings in your email program.
If you previously had avast 7 you will have needed to change your email program, account settings to allow avast to scan SSL email, these changes need to be reversed, e.g set back to the SSL ports and Authentication.
Delete the entries for your email accounts in the avast Mail Shield > Settings > SSL Scanning.
Whilst this support page is for Configuring Thunderbird and avast! Mail Shield.
There is a support page about configuring Thunderbird:
http://www.avast.com/faq.php?article=AVKB91#artTitle
It should point to corresponding areas in Eudora to remove the old certificates.