Below list specifies all possible message flags, as defined in IMAP specification. All of them are pretty self descriptive.

For Recent flag it is important to say that it should be set only for messages that arrive before *anyone* from *any client* opens selected folder. No matter if such message is read or not - Recent flag should be lost immediately.

When message has Deleted flag, this means that when client executes Purge or Expunge on his client, this message will be deleted (but not sooner). You will notice that some clients, such as Mozilla, never actually delete messages from folders. Rather, they move it to Trash folder.