Yes and I live in Arizona and mailed in my ballot for the 2016 election. The point is not that it is possible to do some mail in voting. The point is that it isn't ridiculous to think that mail in voting could be succeptible to fraud. Certainly not so much so that twitter should be trying to influence an election in this way.

There are lot of interesting rules about such ballots. For example, some states do not count them at all unless the margin of victory is less than the number of eligible or returned absentee ballots.