In this case, the attackers target POST customers. They claim that the recipient paid an invoice twice.
This way, the attackers want to bait the user into clicking on the malicious Rembourser maintenant button which redirects to the phishing form.
Note that the FROM header looks legitimate (contact@post.lu), and a CC header (contact@post.lu) is included. Both headers are spoofed in order to make the message more believable.
If you are uncertain about the authenticity of an email, do not hesitate to contact the entity that seems to have sent you the email using a safe communication manner, using the phone for example (no phone number from the untrusted email must be used in order to verify the authenticity).
If you are working for the Luxembourgish government or are using any of the GOVCERT.LU services, it is important to forward phishing emails to us (using Reporting an incident or the Outlook button). This will allow us to take down phishing websites and protect members of our constituency.