Although SMTP operates at the application layer, it is a protocol, not a computer software deal. A mail server (generally Unique software package managing on a devoted device) implements SMTP to talk to other servers. This occurs until finally the shipping is effective or until the e-mail goes again https://www.upwork.com/services/product/development-it-your-company-s-private-network-vpn-setup-for-remote-work-1447284676343549952?ref=project_share&tier=0