I do not think this feature is available right out of the .NET box, but feel free to correct me if I am wrong.

In the detail view of Outlook there is a way to group my messages by the day they were received and I can expand/collapse that group by clicking on a +/- ro the left of the group title.

Has anyone seen an implementation of this along with some source code perhaps?

(I'll try to google for it as soon as I figure out the keywords to search for :)