Poco Reading FAQ - Grouping Messages by Sender

Q:I'd like to group received mail by the sender in my mailboxes. Seems like I saw that somewhere and then lost it. Is it possible? The order doesn't matter. I'm trying to cut down on mailboxes and if I could group the ones from the same sender in one mailbox that'd do it.
You will have to turn off threading to achieve this, then simply click on the "From:" entry in the header of the mailbox index. At the present time Poco won't retain the sort order from invocation to invocation so you will have to do so each time you start Poco.

You can also filter by sender temporarily. Hold the Alt key while you left-click in a column. Poco will filter out all messages that do not share the property you clicked on. So if you click on "joe@domain.com" in the From column, then Poco will show all messages from Joe and hide the rest. This is basically a shortcut to certain functions of the Show Bar.