Excuse me, but there's no icon too when receiving e-mail.
Here is some precisions.
I've started the computer with user A ( avast stats with Windows XP french Home Edition ).
I've changed from user using "Windows" key + L. From this user, I've send an e-mail with attached files ( 2 files for 200 K ). Result : no icon.
I've changed the user to A. The messages are well received ( icon in the systray when analyzing them ). I've replied to the message ( icon in the systray when the messages are sent ). No problem.
Return to user B : no icon when receiving the messages.
When changing from user, the settings are not changed.
When the messages are received by user A, in the header, I have "outbound message clean" and "inbound message clean" telling me that Avast has scanned the message and there's no virus.
I hope it can help. Sincerely.