What does "status" in my folders (inbox, sent messages etc.) mean?

• What does "status" in my folders (inbox, sent messages etc.) mean?

- This message is unread.
- This message was deleted unread.
- This message was read and deleted.
- THis message was replied and deleted.
- This message was replied.
- This message was read.

• What does the envelope next to my inbox mean?
  It means you have new messages ...
• Are sent messages deleted at the inbox of other members, if I delete them in my folder "sent messages" ?
  No, of course the messages will stay in the inbox of the recipient until he deletes them himself ...