Disable sending emails

Hi, I’d need to use mailinabox to allow to receive only, I do want to disable the possibility of sending mails.

Don’t give any account passwords away, and nobody can send.

People need to use their malbox to receive only, so they need accounts

You could disable sending at the firewall level. Attempts to send will fail.

You could also set the SPF record to v=spf1 -all, DMARC to v=dmarc1; p=reject;, and make a custom DKIM record with a fake key so checks always fail. Note this breaks sending for the domain as most servers will send to spam folder no matter what or reject the messages without delivery.

Isn’t there like a built-in function, to change ACLs authorization per mailbox?

Not that I’m aware of. This isn’t a common use-case.

Isn’t there any other option instead of changing firewall rules?

You could make the appropriate modifications to /etc/postfix/main.cf and/or /etc/postfix/master.cf.

Oh, and you can always automatically forward mail to an account to an external mailbox using the sieve rules available through Roundcube filters.