Management folder Assistant mailflow

There is a pretty good article about MFA that explains how it works http://guides.wmlcloud.com/technology/microsoft-exchange-server-2013---how-the-managed-folder-assistant-implements-retention-policies-(part-1)---behind-the-scenes-with-the-mfa.aspx 
One question. 
How exactly does MFA move emails to archive mailbox? Does it use SMTP or any other protocol?