Can you provide links with information on countries that have discovered election fraud and banned mail-in voting? I could not find anything with a quick google search.
In the UK we did discover some postal voting fraud in a 2014 local election in an area of London called Tower Hamlets. We did not ban postal voting as a result.
We have, however, imported a voter ID law from the US which was recently passed by the Johnson government, despite no voter impersonation occurring in Tower Hamlets (or anywhere else really). Previously, no ID was required.
Many other countries have mandatory IDs anyways, so in these cases ID presentation isn't problematic. The issue with ID verification is when only people with eg. a driver's license have IDs.
I think the majority of "postal voting fraud" in the UK consists of very patriarchal families in which the father directs family members as to how to vote, and submits the votes himself. Arguably, this isn't much different from persuading people to change their voting intentions, which is entirely legitimate. Postal voting used to be restricted to people who could show that they were unable to vote in-person, e.g. because they were in the armed services.
I disapprove strongly of that patriarchal practice; but (1) I doubt it has much effect on outcomes, (2) mandatory in-person voting wouldn't prevent it (the patriarch can still instruct his family members).
I also disapprove of early voting. I believe that to cast a vote legitimately, you have to pay some attention to the hustings and the arguments. That is not a barricade I will die defending, though - the tide is against me.
AFAIAA, the UK has not imported a voter ID law from the US. There was a trial at the last election, in a handful of constituencies, and there is mandatory photographic ID for voting in Northern Ireland. A voter ID law was proposed in the Queen's Speech, but no legislation has been tabled or debated.
For the most part, voters receive a poll card in the post, which they don't have to produce at the polling station. You can just turn up, state your name and address, and cast a ballot. Your name is then crossed-out in the voter register, so that the same name-and-address can't vote more than once.
We have, however, imported a voter ID law from the US which was recently passed by the Johnson government, despite no voter impersonation occurring in Tower Hamlets (or anywhere else really). Previously, no ID was required.