Lux Trust - What is It?

You would need to provide more info - who the email is from?, was it a reply you sent to someone? Is it possibly spam? etc, etc.
www.luxtrust.lu/en
Lux Trust is an authentication company in Luxembourg which provides identity security for people and companies, a Lux Trust certificate could be a SSL certificate but that's speculation.
Anyways you would have to provide more details to hazard a guess.