Replying to an encrypted email as encrypted, automatically.

How can I enable all emails sent to me, that are encrypted, so that I reply with Encryption automatically (I.e. I don't have to manually click the lock)? I don't want "Encrypt by Default" enabled, as I don't want ALL my emails to be encrypted automatically, just those that have been initiated with encryption.

I'm unsure if this is managed by my companies MDM, Exchange or within my iOS.