G Suite (Google E-mail) Users
Protect your e-mail by forcing your employees to enrolling into 2-step (2-factor) authentication, enabling this provides a SOLID block from hackers attempting to access your accounts. You should take this seriously. Hacked accounts can damage your business reputation among many other negative things that can happen as a result.
- Enrolling your domain in 2-step verification, which offers an additional layer of user authentication: https://support.google.com/a/answer/175197?hl=en
Completing the Gmail Security Checklist: https://support.google.com/mail/checklist/2986618?hl=en&rd=1
Additional Information about the activity of affected user accounts can be obtained by using the Audit API: http://code.google.com/googleapps/domain/audit/docs/1.0/audit_developers_guide_protocol.html