NO, copying that cert only applies to dovecot mail connections. All users will connect to the main server’s mail domain. They wont connect to their own domain to check mail.
For the mail cert they are seeing imap.example.com and email address as postmaster@example.com on the cert details, which would indicate lets encrypt even though its installed for that domain.
I susspect i’ve not set the right button.
i have a dns domain with lets encrypt
and all the standard domain accounts with the let encrypt ssl cert
Should i add mail.actual.com as well for the domain ssl lets encrypt?
The way I do it is the mail server has its own hostname, lets say mail.mainhost.com with a certificate (postfix and dovcot) and all users connect to the mail server. Doesn’t matter what the user domain is or whether or not their domain has a certificate. The mail server handles all mail for all domains on the box.
MY previous “NO” isn’t actually right. Technically copying that cert to dovcot affects and works for all 6 domains. But in actually, its just 1 cert for the mail server and has nothing to do with certs for domains/virtual servers. No you dont need mail.actual.com for each domain. Separate mail server settings and user-domain settings in your head. They are completely unrelated. Well not really but virtualmin handles the go between.
Same goes for your first question about webmin. Copy that cert to webmin should be yes. users will connect to mainhost.com:10000 to administer their stuff and it will be a valid cert. If users connect to user-domain.com:10000, they will see an invalid cert unless they specify https://.