In Estonian parliamentary election, 44% of the ballot was cast using e-voting

Voting online, or i-voting, as it is often called in Estonia, takes place during the advance voting period that runs from the 10th until the fourth day before the election. SEE: Cybersecurity in an IoT and mobile world (ZDNet special report) | Download the report as a PDF (TechRepublic)
Also, from the 2015 parliamentary elections, i-voters can check whether their vote was received by the server, using a device that has to be equipped with a camera and an internet connection. The first elections when Mobiil-ID was used parallel to ID-card and traditional ballot voting were the 2011 parliamentary elections, when altogether 140,846 votes were made digitally.

Source: www.zdnet.com