Postal Voting vs. Advance Voting
In spite of the Danish term for this procedure literally being "postal voting" it does not refer to a situation where voters can send their votes with the traditional postal service. The Danish authorities therefore prefer the term "advance voting," since it conveys the central feature, i.e. that this kind of voting must take place before Election Day. The advance voting takes place under the auspices of Danish authorities or vote receivers appointed by the Danish authorities to perform this task and with material procured by the Danish Ministry of the Interior and Health.
The term "postal voting" refers to the fact that the votes which are cast in a controlled environment are sent by regular mail by the vote receiving authorities to the relevant Danish municipality where the voter in question is resident.
Who Can Vote in Advance
Everybody on the electoral register who is not able to appear at their polling station on election day during voting hours. Since voters are not allowed to vote at polling stations other than the one where they are designated according to the electoral register, some people would not be able to vote without the possibility to vote by mail, e.g. if they are at work, hospitalized or on vacation abroad on election day.