The voucher can be redeemed until 31 May 2025 when registering a new private email account on the Premium or Standard plan. It is entered in the second step of registration and automatically credited with your first payment for a term of 12 months. Instead of paying for 12 months, you only pay for 6! The first month is generally free. A change of plan is only possible after the 12-month term has expired. The voucher is non-refundable, cannot be cashed in, and cannot be transferred to existing accounts

So it’s 50% discount in case anyone wonders. Standard plan is 3€/mo (so I guess €18 for the first year), premium is €9/mo (so i guess €54 for the first year). There is also a lite plan for 1€/mo but then you don’t get a discount.