I don't see what Avant has to do with the problems email scanning occasionally causes in Windows Mail.
In most antivirus programs that scan email, any problems caused in Windows Mail are rather slow to appear, often taking months for any problems to become visible. Therefore, just one person's experience with a certain antivirus program using email scanning without problems isn't enough to prove anything.
At least avast! allows you to use a custom install where you tell it to leave out the parts that scan email. Therefore, I often recommend the use choose either avast or one other antivirus program that allows such a custom install for Windows Mail users who have to abandon a Norton, McAfee, or Trend antivirus program due to the problems they cause in Windows Mail. A few other people at
<http://www.microsoft.com/communities/newsgroups/list/en-us/default.aspx?dg=microsoft.public.windows.vista.mail> do this also for the same reason.
Anyone wanting to test this might need to use an email server with a significantly higher percentage of messages containing viruses than usual, since I've seen some people report that the problems are most likely to show up when an antivirus program scanning email decides that the email message must be blocked or at least takes longer than usual to decide this.