"Email delivery is unbelievably unreliable and should not be used as a mission critical business tool."
That's almost totally incorrect.
Email is (usually) a extremely reliable transmission method with notification when things go awry. Usually if things just disappear it's because of a fault at the very start of the chain or at the very end - I've seen some mail-servers (not just Exchange) 'successfully' deliver email to a user's mailbox when actually just putting it in the local bit-bucket. This is the email equivalent of the dog shredding your mail after the postie has put it through the door.
When mail disappears in transit, it is usually because some 'intelligent' spam or content filter has taken exception to the message (or error notification) and binned it. This is (IMO) intentional breakage of the system rather than unreliability. It's not the post-office's fault if you deliberately disregard your bills.
If sites or mail servers en-route disappears, then mail will be queued and regularly re-tried. If, after a while (usually several days) delivery is abandoned then an error notification is generated and sent back to the sender.
Mail is designed to be a reliable system. It takes a significant (or extremely unlucky) network and server breakage to just lose mail in transit. What it is not designed to be is instant or even fast. It's a measure of it's success and reliability that many people assume that it is meant to be instant.
If something is business critical, it is likely time-critical and in which case email is not the solution (and should be followed up by a phone call, which is instant) but otherwise it is one of the best methods to communicate in long form.