NNTP (Network News Transfer Protocol) protocol filter.
OT_NNTP_ARTICLE - incoming news message
OT_NNTP_POST - outgoing news message
Indicates object parts:
The objects contain a news message in one stream.
During receiving an incoming message for filtering (not in read-only mode) the library sends X-WAIT: 0 custom header to mail client each 15 seconds to avoid breaking the connection by timeout. These headers are ignored by NNTP clients.
It makes sense to use FF_READ_ONLY_OUT flag, because the news clients usually have
small timeouts, and can break the posts during filtering a large message in dataAvailable