All email communication from RS is done via SMTP. For email systems that are MAPI-based, they should have some SMTP gateway to send to directly (I'm fairly sure Notes has one).

If there isn't, a possible workaround would be to use the SMTP service on an IIS box send emails from RS directly to it.  I highly recommend avoiding this -- SMTP services are a high-profile hacking target.  If you have to use it, make sure it is behind your company firewall and not exposed to the Internet.

You should be hard-pressed to find an email system that doesn't have some means of accepting emails via SMTP.  It may require an add-on or additional configuration, but all of the should have *some* method of doing so.

Thanks for the feedback, good question!