Custom web apps using SMTP server of Hosted / Private Exchange products

Hi! We've got a dedicated server and would like to have an additional email server. Our primary reason for it: we want our custom web apps to be able to send e-mails on behalf of the domain names we control. In other words: we have multiple web apps under multiple domains, and these web apps need to be able to send emails using those domains. So we need an SMTP server solution first and foremost. We are hesitating whether the Hosted / Private Exchange products would be suitable for that, since they are of course more about something else: offering email accounts using email clients.

So any advice / experiences about using the SMTP server under the Hosted / Private Exchange products by one's own custom web apps? No problem? Bad idea?

Hope I'm making sense. Cheers.