Well known and successful in its former iteration, the latter was acquired by the former in late 2007. Rebranded Mailtrust in early 2008, the company has spent the months since adjusting to life at the top of the web hosting food chain, so to speak.

Deepening an existing partnership with Rackspace (a Webmail.us reseller as well as the company's hosting provider), which ultimately led to the acquisition, was the path the company chose from among several alternatives, including seeking outside investment from venture capital type relationship.

"From a product standpoint, the merger made a lot of sense," says Patrick Matthews, president of Mailtrust. "Merging with Rackspace allowed us to think bigger, because we had more resources immediately. And by having more resources, and really stepping up our focus on business class email, that led us into Exchange hosting."

Hosting Exchange was one of the steps that led Mailtrust to the state of differentiation its product currently enjoys in the hosting business - a combined offering featuring both Exchange and the company's house brand Noteworthy that, while not entirely unique in its two-product nature, is unique in its ability to provide either offering on a per-user basis.

From a customer's perspective, the big advantage of that per-user provisioning, says Kirk Averett, senior manager of products at Mailtrust, is price. An Exchange mailbox runs about $14 per month at Mailtrust, whereas a Noteworthy mailbox retails for about $3 per month. The ability to buy Exchange for just those users that require it, and Noteworthy for the rest, can mean a pretty significant savings, even at a small business with just a few mailboxes.

"On average, with us, businesses save about 40 percent as opposed to just buying Exchange for everybody," says Averett.

The relative price of Noteworthy isn't an indicator of its relative features, says Averett, who estimates the in-house software has about 80 percent of the features of Exchange - though it lacks some of the more advanced collaboration features of the Microsoft product.

Nor should the relative price of Noteworthy be considered a measure of the relative quality of the software. Despite the recent inclusion of Exchange, and the advent of its unique per-user hybrid model, Mailtrust still considers its proprietary email product the company's biggest competitive advantage.

"When you compare it to other third-party mail hosting platforms," says Matthews, "we believe Noteworthy is more advanced than 98 percent of the competitors out there. When you're comparing the complete solution, or Noteworthy by itself, against much of the competition, we typically will win from a features and a product standpoint."

Expertise on both platforms, however, is key to the Mailtrust offering, which has its foundations solidly in the choice it offers. On the Noteworthy side, that expertise is the obvious by product of being the company that developed the platform. But on the Exchange side, too, Mailtrust employs David Bjurman-Birr, who Matthews and Averett say is part of quite an exclusive certification level colloquially known as an "Exchange Ranger."

Averett says the deep expertise on both platforms, and the company's efforts to make the platforms work interchangeably and collaboratively within its own solutions, is very difficult to do well, and is either too difficult for many smaller providers to pull off, or goes against some of the business objectives of larger companies like IBM or Microsoft itself, which have their own platforms to promote. Mailtrust believes it has the two best products, each in its own space, which enables it to provide users with a useful choice.

"To me that's always been sort of the promise of the Internet and Web 2.0," says Averett. "You take the best things from different places and mix it all together and you come up with something that's a great fit for you and the way you do business. I just see this as a really powerful approach to that kind of idea with email."

Rather than installing any broad new philosophical foundation, the acquisition by Rackspace - a company that makes a point of being known for its "fanatical support" - Averett says the deal illustrated some valuable similarities in the way the two companies do business, with Mailtrust's support efforts meshing well with the overall Rackspace message, and in certain cases adding a crucial new channel through which Rackspace can influence its customer relationships.

"It's been a great process and a nice fit in a lot of important ways," he says. "I've definitely learned the value that email has to the general server hosting side of the business."

Perhaps surprisingly, adding email services to the relationship with existing Rackspace customers can have a marked impact. According to Averett, among Rackspace server hosting customers - many of whom spend hundreds or thousands of dollars per month on the service - when those customers also have email, the churn rate is about 20 percent lower. That's by adding a product they might spend $20 or $30 per month on.

Averett feels that's part of the power of a hosted mail solution for a hosting company.

"I think there's a subtle thing that happens there. Email, by definition, is something that you use all day long," he says. "If that experience is a good experience, it builds in your eyes the reputation of whomever it is you're working with, very quickly.