Moderators can ask someone from the SE community team to look into it, and they can see individual votes and invalidate votes between certain users. The only cases where this actually happens are users using sock puppets to upvote themselves, colleagues/friends/family going through every post and upvoting everything or users targeting a specific user with a large number of downvotes.

The one thing they all have in common is a larger pattern of votes. SE does not act on individual votes, and emailing them about those is a waste of time.