Bitfields for DESQview mailbox object flags:
Bit(s)	Description	)
 0	all mail messages in common memory
 1	allow write even if closed
 2	don't erase messages when mailbox closed
 4	(DV/X) append messages with like status and sender (stream-oriented
	  mail)
 5	(DV/X) store mail in expanded memory (pool grows as needed)
 6	(DV/X) make mailbox into non-owned mailbox