Fraud is lying to get paid. The employee is lying about their work (generating fake emails to fluff up email counts) with knowledge that the information is used to gauge work done. Their employment continuance, or bonuses, are partially factored based on this metric. Thus, they are lying to get paid. That is fraud.
If a salaried employee lets his boss see him when he comes into the office early, then when out of sight sips coffee and relaxes until his coworkers arrive, is that also fraud? If you caught one of your employees doing that, would you call the cops and report him for fraud?
In some of my previous employers, this type of work was all any employee actually did. Calling it fraud is probably not accurate.
Has anyone ever gotten prosecuted for brown nosing by shifting email times?
Calling that fraud is about as accurate as calling an otter a pencil.