Why are the results of mail in voting so different that in person voting?

Can American trust mail-in voting?

During the Virginia governor’s election, there were nearly 284k “early mail-in ballots,” according to¬†NBC national news. One out of every ten ballots was an early ballot. NBC National News is reporting the same trend in New Jersey.

While Young kid won the Virginia election overall, he only got 24% of the early mail-in ballots.

The question remains. Can Americans have faith in lenient “early mail-in voting.” when they yield skewed results like this:

Traditional in-person voting: Young kid 60%, McAuliffe 39%
Early in-person voting: Young kid 46%, McAullife 54%
Early mail-in voting: Young kid 24%, 76%

Early in-person voting is skewed to McAullife because most locations are usually in urban, heavily Democrat areas. However, the results of early mail-in voting are so wildly skewed it is hard to come up with a clear justification for it. How can we be confident that large-scale ballot harvesting did not take place?