chore: Disable smtputf8 support in config directly (#3750)

* chore: Disable `smtputf8` support in config

This was always configured disabled at runtime, better to just set explicitly in `main.cf` unless config diverges when Dovecot is enabled to opt-out of this feature.

CHANGELOG.md

@@ -8,6 +8,8 @@ All notable changes to this project will be documented in this file. The format
 
 ### Updates
 
+- **Internal:**
+  - Postfix is now configured with `smtputf8_enable = no` in our default `main.cf` config (_instead of during container startup_). ([#3750](https://github.com/docker-mailserver/docker-mailserver/pull/3750))
 - **Rspamd** ([#3726](https://github.com/docker-mailserver/docker-mailserver/pull/3726)):
   - symbol scores for SPF, DKIM & DMARC were updated to more closely align with [RFC7489](https://www.rfc-editor.org/rfc/rfc7489#page-24); please note though that complete alignment is undesirable, because other symbols might be added as well, which changes the overall score calculation again, see [this issue](https://github.com/docker-mailserver/docker-mailserver/issues/3690#issuecomment-1866871996)
 

target/postfix/main.cf

@@ -5,6 +5,9 @@ biff = no
 append_dot_mydomain = no
 readme_directory = no
 
+# Disabled as not compatible with Dovecot
+smtputf8_enable = no
+
 # Basic configuration
 # myhostname =
 alias_maps = hash:/etc/aliases

target/scripts/startup/setup.d/postfix.sh

@@ -19,9 +19,6 @@ function _setup_postfix_early() {
     postconf "inet_protocols = ${POSTFIX_INET_PROTOCOLS}"
   fi
 
-  __postfix__log 'trace' "Disabling SMTPUTF8 support"
-  postconf 'smtputf8_enable = no'
-
   __postfix__log 'trace' "Configuring SASLauthd"
   if [[ ${ENABLE_SASLAUTHD} -eq 1 ]] && [[ ! -f /etc/postfix/sasl/smtpd.conf ]]; then
     cat >/etc/postfix/sasl/smtpd.conf << EOF

test/tests/parallel/set3/mta/smtp_delivery.bats

@@ -277,6 +277,10 @@ function _successful() {
     --protocol ESMTP \
     --server mail.example.test \
     --quit-after FIRST-EHLO
+
+  # Ensure the output is actually related to what we want to refute against:
+  assert_output --partial 'EHLO mail.external.tld'
+  assert_output --partial '221 2.0.0 Bye'
   refute_output --partial 'SMTPUTF8'
 }