My brother, who has had some issues with his Pearl a few months ago provided me with this address for RIM that he had to use to open trouble tix for whatever his issue was.
i think this is it: BlackBerry Support <email@example.com>, they will create a ticket on recieving the mail..
Here are two docs that I referred to yesterday as well. They are on BIS v2.3 and v2.4. BIS 2.3 BIS 2.4
Both more or less stating the following: Improved support for enhanced Yahoo!® Mail
Synchronization of message status
Full two-way immediate synchronization of message status (read and unread) now supported to and from the Yahoo! Mail inbox. For example, if a BlackBerry smartphone user reads an email message from a Yahoo! Mail inbox, the email message is automatically marked as read on the BlackBerry smartphone as well.
Note: Full two-way synchronization of deleted email messages was an added feature with BlackBerry Internet Service 2.2.