Select newly inserted messages (FUMLUB)

In [Options/Prefs window] > Penelope ...

If you select this option, the first message of the most current block of unread messages is highlighted in the Table of Contents window whenever a mailbox is opened. (For mailboxes that are already open, the highlight position will not change.) FUMLUB means First Unread Message of the Last Unread Block. For example, you may have a series of unread messages in a mailbox scattered throughout your Table of Contents. The first message of the last block of unread messages listed in your Table of Contents is selected.