Marketing Land really nails it in their article "Can A Hybrid Email Sending Strategy Give You The Best Of Both Worlds?" In this post, Steve Dille suggests using both an ESP (email service provider) and an in-house system in hybrid - keeping your "e-blasts" in the cloud with your favorite provider (e.g. ExactTarget, Constant Contact, MailChimp, or whatever), while employing database-driven emails in-house for greater efficiency and immediacy.
I've been an advocate of this approach ever since I first got involved in automated marketing and triggered messaging. Transactional and triggered messages rely entirely on immediacy, and because the volume of these emails is so low, deliverability is rarely an issue. Marketing automation and highly targeted messages tend to be deployed in lower volume blasts as well, and with the specific requirements and needs of each, setting up appropriate rules for such messages within an ESP can become a challenge.
A DUAL SOLUTION
One thing this article failed to mention is that most business-oriented ESPs will let you use them dually as a cloud solution as well as a stand-alone mail server for any of your in-house systems. By using your ESP for both purposes, you can reap the benefits of the many features they offer, such as consolidated analytics, best practices in delivery optimization, and centralized bounce and blacklist management.
I'd be remiss if I didn't mention that Kentico EMS is a platform capable of consolidating your marketing automation, website transactional messaging, and triggered messaging all into a single solution.
Has your business had success with employing a hybrid email solution? Let me know about your take on this.