UK has universal mail-in-voting for any reason.
Some US states also have universal mail-in-voting, and have done for some time.
The counterpoint to "make sure elections don't have sources of fraud" is that you need to strike a balance - the right to vote is sacrosanct (and in some cases was hard won) so any laws that pretend to be about election integrity, but are in fact a way to suppress voting in certain demographics are arguably more dangerous than the exceedingly low levels of fraud that elections have.