First introduced in the late 1970s as an effort to boost low voter turnout, postal voting was anchored in Swiss law in 1994. By 2006, all 26 cantons had introduced functioning systems.

“It works well, so there’s not much debate about it,” says Uwe Serdült, a political scientist at the University of Zurich. Cantons report that around 90% of citizens now vote by post, and some have reported figures up to 97% (Aargau, 2017). There were debates about security in the early years of postal voting, Serdült says – as there are now around e-voting. But over the years it has been accepted, largely due to the high levels of trust in Switzerland – “vis-à-vis the state, and in the postal system”.

https://www.swissinfo.ch/eng/politics/how-the-world-s-most-frequent-voters-handle-postal-ballots/46070666