Most of the examples shared with us were a result of spam and can be simply ignored. If you received a valid submission, the case will need to be manually created using the data in the email attached to the error notice.

You might also consider having your mail server filter out malformed email addresses or creating a rule to handle these error emails if you receive large volumes due to spam.

This is by design as Salesforce requires a properly formed email address in email fields such as SuppliedEmail.