Something I would appreciate, even if there are many courses, they are not completely good, not like Jay can do them. It would be to set up MailCow and configure it correctly, with all the security and settings. Could be like Proxmox where there are a few sections. As you learn, you want to develop more. and now the curiosity is starting to get to a mail server, even if many advise against it.
Why not just postfix and dovecot?