Dovecot quota support would log auth failures when Postfix validated incoming mail to accept/reject and the `check_policy_service` for `quota-status` was queried with a recipient that was an account alias.
When Dovecot is not aware of the user account, it will not be able to check a quota and inform Postfix that everything is fine, Postfix will accept the mail and send it to Dovecot, where if the quota is exceeded will result in a bounce back to the sender. This is considered "backscatter" and can be abused by spammers forging the sender address which can get your server blacklisted.
The solution is to either disable quota support `ENABLE_QUOTAS=0`, or as a workaround, add dummy accounts to Dovecot userdb for aliases in `postfix-virtual.cf` (not `postfix-aliases.cf`), these dummy accounts will map to the real user account mailbox (real users are defined in `postfix-accounts.cf`).
The workaround is naive, in that we only check for basic 1-to-1 alias mapping to real accounts. This will still be an issue for aliases that map to another alias or multiple addresses (real or alias). Unfortunately Postfix will not expand aliases until accepting mail where this would be too late.
A better solution is to proxy the `check_policy_service` from Dovecot `quota-status` that Postfix queries in `main.cf:smtpd_recipient_restrictions`, however this requires a fair amount more of additional work and still requires an implementation to recursively query aliases for nested or multiple address mappings, which can then be forwarded to the `quota-status` service configured by Dovecot in `/etc/dovecot/conf.d/90-quota.conf`.
LDAP users are unaffected as quota support is not supported/implemented with `docker-mailserver` at this time, it is always considered disabled when using LDAP.
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Additionally Dovecot configuration for `passdb` has been fixed to use the correct password hash scheme of `SHA512-CRYPT`.
Co-authored-by: Casper <casperklein@users.noreply.github.com>
Co-authored-by: Brennan Kinney <5098581+polarathene@users.noreply.github.com>
