I know the X headers are not standard but "X-Auto-Response-Suppress" is a widely used one. Even our Redmine sends mails with that header. So it'd be really great if the plesk auto-responder could ignore emails with that header if its value includes "OOF" or "AutoReply".
See [MS-OXCMAIL]: Auto...
Our customer's data privacy officer was asking about that - so I guess we'll have to hope he is okay if I tell him that we "cannot disclose that information" or something like that...