I have setup iRedmail from https://www.linuxbabe.com/mail-server/ubuntu-18-04-iredmail-email-server. So far, running well.
I want to know how to setup bounced email sending to sender inbox when an email fails to send ? Currently my users don't have a way to get notified.
iRedMail is using Postfix as MTA, so you may want to configure bounce related settings there. See the The Big Picture to learn how everything interacts.
See https://www.howtoforge.com/configure-custom-postfix-bounce-messages for a easy-to-follow howto on configuring bounces in Postfix.
For further common questions, please see the extensive howto section of iRedMail.
