1. Government server - whatever the gov sets up. Chief attribute(s): security
2. Private sector email provider - a service like hotmail or gmail. Chief attribute(s): convenience and security.
3. Personal homebrew server - something on a box you hire someone to set up for you. Chief attribute(s): control and convenience.
A public servant who would use #2 for testing purposes so that they can execute the duties of their jobs is one thing. A public servant who would go to the lengths needed to secure #3, thereby placing their complete archive beyond the reach of the public but well within the reach of intruders, has in my view used their public office for private gain at the potential cost of national security. Their motives and judgment are entirely dubious.