Ask HN: Why do some of the engineers/hackers manage their own mail servers?

I want to know why do some engineers/hackers have email setup on their private domains. I like most of the people use gmail. Is the desire to learn how to manage the system makes people have their own private mail servers? I don't really see security or privacy as an issue unless gpg is used extensively.

Do you configure/setup/manage the mail servers yourself or is it handled by the hosting service providers?