Postfix
Postix - Open source email server for Unix, IBM Public license.
Postfix Add Mailbox
1) Login to Postfix. e.g. https://mail.opensourceecology.de/
2) Choose "Add Mailbox" from the main page
Final Message
Email sent! The mailbox has been added to the mailbox table, but none (or only some) of the predefined sub-folders could be created.
Thunderbird
Receiving and sending emails with Thunderbird works.