Ok so it sounds to me like the client (in this case the business app)
should be adding the date in the header, BUT SMTP servers must not
reject emails based on no date in the header.

I think I'm getting closer (or possibly not!!)

Right - the biz app should do it, but if not then the smtp server that
accepts it should do it. I personally think outlook should since it is
handing it off, but apparently its getting dropped into the outbox in
such a way that outlook can't add it.

The server shouldn't 'should' do it, the server should 'may' add it.

Horrible grammar, but I think it's vaguely clear.

Basically, the server doesn't have to add it, there's absolutely no rule
saying it should, just that it can. I'd argue that it shouldn't do it, but
since the rules don't go either way, we're both right.

And I agree about how its getting into the outbox. In fact, lets reverse
engineer it.

The Date field is actually set by when the client submits a message into
the queue, not the server queue but the local queue. NNTP messages are the
same way, you reply offline at 10pm, but don't sync until the next day at
7a, all the posts come in with 10p timestamps (or should, last I checked).

So, the 2822 header must get built somewhere in the clicking of the 'send'
button (or alt/ctrl-enter). Whatever internal code is being called gets skipped
by the business app which just drops into the outbox.

So, your app is letting Outlook do the mailing, making your app not the user
agent, but leaving Outlook to be the user agent. Which means Outlook is responsible
for adding the date.

However, whatever method you're using to get the message into the Outbox
seems to circumvent the code that creates the SMTP header. I don't see an
easy way to get to the Internet Headers via the gui for a message in the
Outbox to verify this, so you might want to pop into one of the coding forums
to see if there's a way to get this to work better.

Or, conversely, just configure your app to not use Outlook and just speak
SMTP and actually be the user agent.

--
f.h.
Microsoft Outlook MVP