Emails tend to leak easily. I keep a server to track such leaks, one email per service. I'm using Modoboa, but it is limited due to its complexity. I'm not sure I can reinstall it with certificates, backups and more being OK.
Issues with keeping an email server
Hosting providers are bokers and block the email-related ports on the VDS servers
The general complexity of email stack prevent you from having extensive control and making backups
I wish more people were responsible for their own security, as that'll lead to a mutual benefit
First, I have doubts on Postwhite's architecture and want to rewrite it