The possibilities of placing a thumb on the scale are much greater with a mail in ballot system.
First you have to have a group of individuals who are motivated to take the risk of tampering with the election.
Once you have a team put together you begin collecting ballots.
1. Some ballots may be collected by placing fake ballot box drop offs. Some can be collected thru insiders (your guys) working at the USPS. I'd work out a drop off location for the USPS worker to dump ballots then have one member go pick them up. Could be a dumpster in a city or a rural location if outside a major population center.
2. Some can be stolen from mail boxes.
3. Set up teams to go into retirement homes for the elderly, help those people vote in some cases in others just collect their ballots and fill them out how you please.
4. A few individuals can be tasked with identifying the deceased voters that are still registered and request a ballot for them.
5. Names and dates of birth/death can be found at any cemetery. The dead can still request ballots and or vote long after being in the ground.
6. Mass produce counterfeit ballots, enter the names and birthdates of deceased voters. Fill them out though one could understand that this would be labor intensive and therefore limit the completion of ballots to just a check in the box for one candidate only. This is also safer than requesting a ballot thru the mail.
7. Poll workers. You'd need to recruit poll workers or place members of your team in key positions during the ballot counting process. Those members could weed out the unwanted votes by spoiling the ballots in some way.
8. Multiple ballots received in the mailbox. People that received multiple ballots from the individuals that previously resided at that address could fill out those ballots and mail them in. Who'd know?
Those are just a few off the top of my head. When voting occurs in other ways besides in person it's easy to cheat. There's literally no risk of getting caught.
Rudy, is that you?
Belongs here.
No, wait . . . here.