This function reopens the specified stream to a new mailbox on an IMAP or NNTP server.
The options are a bit mask with one or more of the following:
OP_READONLY - Open mailbox read-only
OP_ANONYMOUS - Don't use or update a .newsrc for news (NNTP only)
OP_HALFOPEN - For IMAP and NNTP names, open a connection but don't open a mailbox.
CL_EXPUNGE - Expunge mailbox automatically upon mailbox close (see also imap_delete() and imap_expunge())
如果成功则返回 TRUE，失败则返回 FALSE。