I ignore these emails, or I ask the sender to communicate from a real email address if the issue seems important.  I promise to protect, as I have for a quarter-century now, the identities of faculty or students who are writing to me about matters where they worry they are at risk of retaliation.  I may not post on the blog about these issues, but I will not reveal your identity.  I get these emails with some frequency (one or two a month), and they are not productive.  Thank you.

UPDATE:  Just to clarify, most of the anonymous emails I get are from proton addresses, but not all (occasionally they come from gmail).