I have seen this website provided by Google to learn more about privacy and safety measures online: https://beinternetawesome.withgoogle.com/en_us/interland

Something that classes could use is a spam folder on Gmail. The algorithms within the email services usually report suspicious email addresses as spam. This way, the teacher could make a few suspicious-type emails and show how Gmail would categorise them (this would require some testing beforehand though). This could also be used just through a manual set-up where students themselves are a categorising agent to see which emails might be linked with suspicion and which might be safe.