[AccessD] SMTP or Outlook?

Dear List:

I am developing a legal matter tracking app for a client. One of the
features is to email reports on a regular schedule to clients regarding the
various matters being handled.  

We can go with either Outlook or SMTP.  There's already some SMTP code in
the app (legacy app) and I've got some code for Outlook.  

Outlook, of course, has the disadvantage of thae nag messages requiring you
to allow access to Outlook when sending from another app.  I get around this
by using Click Yes but that has a security problem, obviously, in that
malware could then use Outlook.  

BTW, this isn't just for in-house use - he intends to make this a product.

Any opinions?  Is there a third alternative?

MTIA

Rocky