Postfix: two mail related questions

the .db is generated from the original file without the .db, using postmap. The .db is just a binary, compiled version of the original file, there’s not much point reading it compared to reading the source

Not sure to understand the whole intrications regarding the alias, but yes, sending mails using your alias identity is supposed to work with the default configuration

Can you double-confirm that yunohost tools regen-conf postfix is happy ?