Just uninstall the current version and then reinstall the desired previous version. If you don't have a copy of the previous version installer, you'll have to go out in search of one.
This might also be an opportune time to try a different email client. Mozilla Thunderbird, for example, is the email client that more or less started the whole junk mail filter concept as it's generally known today. It's developed under an open source license, which to you means it, and all of it's features, will always be free. It also doesn't have the Fisher Price feel that Incredimail does.
Foolishly, I "upgraded" to Build 2206. Now, the Junk Mail Filter feature is no longer free ($39.95). Also, now the messages that I want, only open as attachments. This requires opening a new page.
How can I revert to the older version of Incredimail XE? I recveived no response from their "customer support." I have Windows XP. Thanx.