According to EstoniaVoting:
Estonia is the only country in the world that relies on Internet voting in a significant way for legally-binding national elections — up to 25% of voters cast their ballots online. This makes the security of Estonia’s system of interest to technologists and voters the world over. As international experts on e-voting security, we decided to perform an independent evaluation of the system, based on election observation, code review, and laboratory testing
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What we found alarmed us. There were staggering gaps in procedural and operational security, and the architecture of the system leaves it open to cyberattacks from foreign powers, such as Russia. These attacks could alter votes or leave election outcomes in dispute. We have confirmed these attacks in our lab — they are real threats. We urgently recommend that Estonia discontinue use of the system.
as of yet, Estonia have used the e-voting system eight times with binding results.
In 2012 a separate Electronic Voting Committee was established who is now responsible for conducting Internet voting while the National Electoral Committee retains a supervisory role. Internet voting was first introduced in the local elections of 2005, when more than 9 thousand voters cast their ballot via the Internet (this corresponded to about 2 per cent of all participating voters). Today, I-voting with binding results has been carried out eight times in Estonia
With also valid skepticism from individuals within their own government dating back before the release in 2005 on both technical and political issues (Journal of Humanities and Social Sciences)
Still, While Estonia could have easily been the world leader in e-voting by introducing this as a regular feature already for the location elections of 2002, probably genuine worries that technical problems would not be solved by the Fall of that year, as well as the skepticism of individual members of parties generally in favour of e-voting, all of them reasonable and appropriate, were among the reasons that prevented such an outcome. But in the end, it was mainly the resistance of the rural opposition party, which – likewise reasonably and appropriately – feared that such a feature would increase the vote of its competitor parties, and which there would have very rightly and properly fought against it in Parliament, that led to the postponement of actual e-voting in Estonia until 2005.
Is there any public research/statements from the Estonian government (or funded by the Estonian government) to support why they still use e-voting?