Postbox Express Quickstart Guide
The Pending flag within the read/unread column can be used to mark messages that are pending a response, or in other words, a message that requires a response from someone else before you can act upon it. Pending messages can remain within your inbox to serve as a reminder, and they are colored light gray so that you can more easily ignore them in favor of other messages that require immediate attention. The Pending flag is particularly useful for To-Dos that you have delegated to others.
The Pending flag is actually a state that resides within the Read field. Thus a message can have three possible status states: unread, read, and pending.
To mark a message Pending, click within the message list Read column until the watch face appears. When a new reply arrives, the pending flag is automatically removed and the message status is switched to "Unread," thus signifying that new information has arrived and that the message is worthy of attention.