A friend of mine, Raihan-worked as part of my engineer team @ Excellent-learn Haraka since December as an alternative for simple SMTP engine for our tailor-made SMTP Relay. We would like to build a fast, simple, light, highly extensible SMTP server as a replacement for our current postfix or Zimbra.
What is Haraka?
As we are currently using Zimbra LDAP as central authentication, Raihan trying to create Haraka as front-end relay with LDAP authentication against Zimbra. Although Haraka comes with docs, wiki and tutorial out there, Raihan took almost 1 month to be able sending email with TLS auth and make sure everything is configured properly.
You can follow his issue thread and how he finally resolved the problem, here : https://github.com/haraka/Haraka/issues/2760