The postal provisions would place requirements on the ballot RETURN envelope (with the marked ballot sent back from the voter) that it must identify the voter via a barcode for comparison with the approved list. It would apply to envelopes marked as "official election mail", which is not a marking states are required to use, though most do.

Anyway, this will be challenged in court, and the logistics of it would make it pretty infeasible prior to the midterms in any case.

It's worth trying to understand what problem this executive order is purporting to solve. It's not clear; you have to squint.

Trump and many of the election deniers have created a widespread impression that mail-in ballots are unsecured, and that there are no (or only ineffective) safeguards against sending in counterfeit, fake, or duplicated ballots and having them counted.

But, despite being repeated frequently, this impression is completely false and baseless, as I'll discuss.

Mail in ballots have security features and a processing workflow that mirror that of in-person voting. Just about every mechanism that prevents you from showing up to vote in person multiple times or without being registered has an analog - sometimes a stronger one - in mail-in ballot processing.

The precise details vary from state to state and for different voters, but roughly:

1. Marked ballots are generally returned in two nested envelopes or wrappers; the inner wrapper has no identifying information, while the outer one is unique to the voter and has both identifying information and, generally, the voter's signature. In most cases the only way to obtain a valid ballot and envelope is to have it mailed to the address on file with the local election office.

2. The voter returns (by mail, dropbox, etc) their ballot in the two envelopes and signs the outer one.

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3. When the ballot envelope reaches the election office, it's processed in two stages:

3a) First, the outer envelope is checked to verify that it contains the unique identifying information for the voter (usually a unique ID number), that that ballot wasn't already processed, and that the signature matches what's on file. If there is any discrepancy, the ballot is held for exception processing.

3b) If the verification was OK, the inner envelope (with the ballot inside) is sent to tallying.
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4) The inner envelopes (of accepted ballots) are opened only later, in batches after they've been separated from the outer envelopes with the identifying information. This preserves ballot secrecy. Then the opened ballots are sent to the tally machines (generally optical scanners) and retained.

This workflow has a number of important properties.

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- First, you can only send in a ballot accompanied (on the outer envelope) by something that was sent specifically to the voter, with unique identifying information that a third party couldn't obtain (the ballot ID number). And each ballot ID can only be processed once, since it's checked off a list once it's accepted.

- Second, the submitter of the ballot has to sign the voter's signature. So we know not only that the ballot was sent to them, but have a signature to compare it with.

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- Third, exceptions are extremely rare and would be quickly noticed. If an even moderate number of duplicate ballots or ballots with invalid ID numbers were to come it, that would be a HUGE deal (and I'm not aware of any place in the US where it's actually happened). It would rapidly trigger a major investigation, likely involving both state/local and federal authorities.

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So in summary, mail-in ballots are secured by mechanisms and processes that replicate all the steps of the check-in process at in-person precinct polling stations, but with the ADDITIONAL safeguard that the voter needs to provide a unique document that was sent to their address for each election.

The idea that mail-in voting invites fraud is simply not supported by reality.