Do I still need to call mailman.DeleteEmail(email) if ImmediateDelete is set to 1 already?
The ImmediateDelete property affects the behavior of the DeleteEmail method. (It does not imply that DeleteEmail does not need to be called.) The description for ImmediateDelete is as follows:
If true (the default) then any method that deletes an email from the POP3 server will also issue a QUIT command to close the session to ensure the message is deleted immediately.
The POP3 protocol is such that the DELE command marks a message for deletion. It is not actually deleted until the QUIT command is sent and the session is closed. If ImmediateDelete is true, then any Chilkat MailMan method that marks a message (or messages) for deletion will also followup with a QUIT command and close the session. If your program sets ImmediateDelete to false, it must make sure to call Pop3EndSession to ensure that messages marked for deletion are actually deleted.