diff --git a/imageroot/actions/get-configuration/20read b/imageroot/actions/get-configuration/20read
index 49c6366..cb201e7 100755
--- a/imageroot/actions/get-configuration/20read
+++ b/imageroot/actions/get-configuration/20read
@@ -36,7 +36,7 @@ for key in agent.list_service_providers(rdb,'imap','tcp'):
     mail = key['module_id']
     get_retval = agent.tasks.run(f"module/{mail}",'list-domains')
     for kd in get_retval['output']:
-        if kd['addusers']:
+        if kd.get('addusers') == True:
             obj = {
                 "name": key['module_id'],
                 "label": f"{kd['domain']} ({key['mail_hostname']})",
diff --git a/ui/public/i18n/en/translation.json b/ui/public/i18n/en/translation.json
index 1922612..02f5f44 100644
--- a/ui/public/i18n/en/translation.json
+++ b/ui/public/i18n/en/translation.json
@@ -40,7 +40,9 @@
     "choose_mail_server": "Select a domain",
     "choose_the_mail_server_to_use": "Choose the domain suffix used for both identifying and initializing the user account and their mail address preferences",
     "mail_server_is_not_valid": "This mail server cannot be used by Roundcube webmail",
-    "upload_max_filesize_number_lte": "Must be less than 120 MB"
+    "upload_max_filesize_number_lte": "Must be less than 120 MB",
+    "no_available_mail_domain_check_users": "Make sure the mail domain you intend to use has \"Add user addresses from user domain\" checkbox enabled",
+    "mail_module_misconfigured": "No mail domain available"
   },
   "about": {
     "title": "About"
diff --git a/ui/src/views/Settings.vue b/ui/src/views/Settings.vue
index 4995551..1ed3eeb 100644
--- a/ui/src/views/Settings.vue
+++ b/ui/src/views/Settings.vue
@@ -61,6 +61,16 @@
                 $t("settings.enabled")
               }}</template>
             </cv-toggle>
+            <cv-row v-if="mail_server_URL.length === 0 && ! loading.getConfiguration">
+              <cv-column>
+                <NsInlineNotification
+                  kind="warning"
+                  :title="$t('settings.mail_module_misconfigured')"
+                  :description="$t('settings.no_available_mail_domain_check_users')"
+                  :showCloseButton="false"
+                />
+              </cv-column>
+            </cv-row>
             <NsComboBox
               v-model.trim="mail_server"
               :autoFilter="true"
@@ -286,6 +296,11 @@ export default {
         } else {
           this.mail_server = "";
         }
+        // if mail_server_URL is empty, set default value
+        if (this.mail_server_URL.length === 0) {
+          // we want to avoid to save the form, there is no users set in the mail domain
+          this.mail_server = "";
+        }
       });
 
       this.mail_server_URL = config.mail_server_URL;