Increase mail_max_userip_connections for trusted connections

Implement the same configuration of NS7: if the connection comes from a
trusted network (cluster VPN) the connection limit per user is
increased.

This is a workaround for Webtop client, that opens many connections
simultaneously.

dovecot/README.md

@@ -54,7 +54,7 @@ Private TCP ports:
 - `DOVECOT_SPAM_SUBJECT_PREFIX`, default empty. If set, the string is prefixed to the message `Subject:` header.
 - `DOVECOT_SPAMT_PASS`, password for Rspamd API, required for ham/spam training
 - `DOVECOT_TRASH_FOLDER`, default `Trash`. Mailbox folder name where messages are moved when they are deleted.
-- `DOVECOT_MAX_USERIP_CONNECTIONS`, default `20`. Set dovecot `mail_max_userip_connections` configuration parameter.
+- `DOVECOT_MAX_USERIP_CONNECTIONS`, default `20`. Set dovecot `mail_max_userip_connections` configuration parameter. This limit is rasied 5 times for connections coming from trusted networks
 - `DOVECOT_SHAREDSEEN`, default empty. If set, the SEEN flag of shared folders is stored in a `dovecot.pvt*` index file, for every user
 
 ## Logs

dovecot/usr/local/bin/reload-config

@@ -106,6 +106,7 @@ fi
     # Add the user_domain to /etc/hosts to quiet dns queries
     if  ! grep  -qxF '#user_domain' /etc/hosts; then
         # user_domain is not present in /etc/hosts
+        # shellcheck disable=SC3036
         echo -e "\n#user_domain\n${ldap_host} ${ldap_domain}" >> /etc/hosts
     else
         # /etc/hosts is mounted in the container,
@@ -116,6 +117,18 @@ fi
     fi
 )
 
+(
+    exec >/etc/dovecot/trusted_networks.conf
+    echo "# Special settings for trusted networks"
+    # shellcheck disable=SC3060
+    for network in ${DOVECOT_TRUSTED_NETWORKS//,/ } ; do
+        echo "remote ${network} {"
+        echo "    mail_max_userip_connections =" $(( ${DOVECOT_MAX_USERIP_CONNECTIONS:-20} * 5 ))
+        echo "}"
+        echo ""
+    done
+)
+
 if [ -f /run/dovecot/master.pid ]; then
     doveadm reload
 fi