[irrational]

Those are cause for concern, but let's be realistic, the percentage of how many coercive ballots must be very low, I'd guess less than 1%. I think the pros of mail in voting (getting a greater percentage of the population to vote because they can do so at their leisure, don't have to take time off of work, don't have to stand in lines, etc.) outweigh the cons (such as potential coercion or selling of votes).

[bonzini]

There are countries, or regions, or municipalities, or neighborhoods where the number of coerced ballots can easily be 50% or more. Voting by email is a complete no-no in those situations.

There are also countries where turnout is consistently above 70% and there is no mail voting. In the US the obstacles to voting are not having to go to a polling station: voter registration due to not having a federal ID, voting on a Tuesday rather than during the weekend, gerrymandering due to political bodies bring able to affect the redistricting process, and so on.