When you receive new mail, K-9 will retrieve it (POP) or poll for it or receive a PUSH notification about it (IMAP/WebDAV). If so configured, K-9 will use the Android system notifier facility to alert you to the new messages so you can read them.
K-9 will display a notifier on the window-shade for each mailbox which has new messages. When you tap on this notifier, you will be taken to either the Folder List or the Unread Message List for that mailbox/account, depending on the setting of Account Settings->Notifications->Notification Opens Unread for that account. If you have not turned that setting on, you can tap Inbox to be taken into it.
There are two ways of being notified of new mail synchronized to your device, push and poll. Push means that the server notifies you of new email. Poll means you check the server to see if new mail exists.
You can configure synchronization of each folder using Folder Classes.
You can also manually synchronize an account. This performs a poll of subscribed folders.
Various actions may perform a manual poll to ensure that the state is consistent before/after they perform the action.
(‘Sync’ in the app generally refers to polling.)
At this point, you’re looking at a Message List – a list of all (or only the unread) messages in a given folder; in this case, the Inbox folder for that email account. This list will display message titles (in bold if not yet read, highlighted if not fully down loaded), a time or date (depending on the age of the message), and either the sender’s email address or “real name”. It may also display a short preview of the body text of the message, a Star icon for flagging messages and/or a multi-select checkbox, if you’ve enabled those options in Global Settings->Display.
At this point, you can tap on a message in the list to open it for reading, or long-press to get the message’s Context Menu, which contains these options, on a scrolling pop-up menu with the message’s title at its top:
|Shortcut||Message List||Message Details|
|Volume up||next message (1)||next message (1)|
|Volume down||prev message (1)||prev message (1)|
|Back||managed back (2)||managed back (2)|
|g||toggle flag||toggle flag|
|h||show keys help||show keys help|
|i||toggle sort order|
|q||up-to folder list|
|o||cycle sort key|
|u||mark as unread||mark as unread|
|z||toggle read||zoom out|