I did figure out that I could clear the "unsent" flag using simple
MAPI, with MAPISaveMail(), then turn around and use the OOM to set the
rest of the fields. I might end up going this route if I find out
that simple MAPI isn't as buggy as extended MAPI. Since even simple
MAPI can set this MAPI property it almost seems like a bug that the
OOM doesn't give you write access to "Sent" or "Submitted" properties
until the item is saved for the first time.
One weird thing, which might be beyond this newsgroup, is that after I
save the message with MAPISaveMail(), then open with OOM and modify
the "MessageClass" field, the icon for the message shows up as the
icon for the new class, but when I open it it still uses the standard
email form instead of the custom form I have setup for that message
class. However, when I add a new message using just OOM, and no
MAPISaveMail() calls, it uses the correct custom form. Anyone ever
had this problem?