Int 15 Fn 12  - Desqview 2.50+ - Send Message - "readinto" - Get Next Mai  [Q]

   AH = 12h
   BH = 13h
   BL = mailbox from which to read
       00h DWORD on top of stack is mailbox handle
       02h use given task's mailbox (task's handle on top of stack)
       03h use current task's default mailbox
   STACK: DWORD size of buffer in bytes
          DWORD pointer to buffer

Return: STACK: DWORD number of bytes read
Program: DESQview 2.5x is distributed as part of DESQview/X 1.0x

Notes: this call blocks if no input is available, but will return less than
     the requested number of bytes if some (but insufficient) data is
     available
   use this call instead of AH=12h/BH=04h if the mailbox has flag bits
     4 or 5 set, as common memory may be exhausted by that call when
     attempting to read the next message

See Also: AH=12h/BH=04h"READ",AH=12h/BH=05h,AH=12h/BH=16h