One of the difficulties when you have a large number of emails and/or a large number of accounts is getting part way through a review and having a refresh that adds in emails in several different places in your list (i.e. when the list is not sorted by time/date).
Have an option to delay the display of the latest new emails until the existing list had been washed. Then allow the ability to view each download group (grouped by time/date) and to work on those in isolation. This could be displayed as a line in the list pane with download date and time and the number of emails in that group. Obviously if the emails where downloaded by your email software and a group no longer had any emails in it then this group would automatically be removed on refresh.
Cheers,
Nigel
(Nigel Freeney)