Mail in ballots are really really hard to be fraudulent. Ballots taken from ballot dropboxes are kept locked away until whenever they’re allowed to be counted. You cannot canvass them before the law allows

When ballots are opened they’re reviewed quickly to be scanned. Any ballots that ppl didn’t properly fill out are reviewed by adjudicators (could be lawyers but not required) one by one. Both parties can review those ballots to see if they agree what the chosen decision will be

Ballots that go thru adjudication are always added last to ballot batches of results once reviewed by election officials