Just this week, Clinton told the media that it "would have been better" to use a government email address along with the personal one she used while secretary of state.
However, Clinton insisted she did not violate any federal regulation and didn't risk exposing sensitive information by using her personal email server.
In addition to likely presidential frontrunners, there could be other Americans interested in building private email systems. It isn't that complicated, at least for the technologically savvy, but it can get expensive and the benefits aren't clear cut.
To start, users need to buy a server, which can cost about $500. Companies such as Lenovo sell them. These are relatively small machines that don't require much power.
After that, you'll need the software: an operating system and mail system that companies such as Microsoft sell. The cost? Under $1,000.
Next up: the system needs to be secured, and this is where it can get expensive if you're looking for the highest level of security. Enterprise-class firewalls and high-end antivirus software can quickly ring up a big bill: $100,000, easy.
Beyond the time and money required to run a system, there's another disadvantage: The owner has to maintain the network. In other words, users have to work as their very own information technology managers, or rely on tech experts to address issues that arise.
"If you have a problem while you're traveling then you would have to fly back, or call somebody to fix the server," said Rob Enderle of the Enderle Group. "And, of course, you would have to give them access to it."
What are the benefits of a private email system?
The owner builds, runs and controls it, potentially granting them a degree of independence and autonomy with their private communications.
"You don't have to share information with anybody you don't want to share it with," said Patrick Moorhead of Moor Insights & Strategy. "If you want to hide an email from somebody then you can do that as opposed to, say, having the State Department IT managers have access to that email."
But, given the associated costs, experts say this technology probably remains attractive to a very small—and very wealthy—group of users such as former secretaries of state.