Even though SMTP operates at the applying layer, It's a protocol, not a application package. A mail server (normally Exclusive software package jogging with a devoted equipment) implements SMTP to talk to other servers. The great thing about SMTP is always that it’s an open protocol. The consumer and https://www.upwork.com/services/product/development-it-email-deliverability-inbox-reduce-spam-dns-issues-fixed-dkim-spf-dmarc-1378055073774727168?ref=project_share&tier=0