Ingrid Lunden / TechCrunch:Mimecast, which makes email security tools, says PE firm Permira plans to take it private in a $5.8B all-cash deal; Mimecast has been public since 2015 — Nine months after competitor Proofpoint was scooped up by Thoma Bravo for $12.3 billion, Mimecast is also going the private equity route.