change messages per PLT-6392 (#6481)

i18n/en.json

@@ -6013,7 +6013,7 @@
   },
   {
     "id": "utils.mail.send_mail.from_address.app_error",
-    "translation": "Failed to add from email address"
+    "translation": "Notification From Address setting is missing or invalid."
   },
   {
     "id": "utils.mail.send_mail.msg.app_error",
@@ -6029,7 +6029,7 @@
   },
   {
     "id": "utils.mail.send_mail.to_address.app_error",
-    "translation": "Failed to add to email address"
+    "translation": "Notification To Address setting is missing or invalid."
   },
   {
     "id": "utils.mail.test.configured.error",