The Cold Outreach Deliverability Playbook: Mastering RFC 5321 Socket Mechanics & Inbound Gateway Bypasses
An engineering breakdown of how modern mail transfer agents (MTAs) and security firewalls (Mimecast, Proofpoint, Barracuda) evaluate SMTP socket handshakes. How to configure custom DKIM 2048-bit selectors, strict DMARC alignment, and eliminate bounce flags before transmitting messages.