02 Ten layers, input to outcome · 11 pages · 14k words
The outbound stack
Cold email is not one product. It is a chain — data, verification, signals and copy going in; infrastructure, warmup, sequencing and multichannel in the middle; replies and agents coming out. Each layer has its own leaders and its own margin.
Inputs
Who to email, whether the address is real, why now, and what to say.
Contact data and enrichment
A verified work email now costs one to two cents from specialist finders, sequencers are bundling 450M–850M-record databases, and Clay is the only player still charging a platform premium.
Email verification
Standard SMTP verification costs $0.50–$8 per thousand and is being absorbed into finders and sequencers; the only part with pricing power left is catch-all verification.
Signals layer
Intent, job-change and website-visitor data that tells you when to email whom. It turns outbound from spray into triggers — and it is US-centric, consolidating, and cheap at the bottom.
Copy and personalisation layer
The tools that write and personalise the email: Clay AI columns, Lavender, Twain, sequencer AI writers and custom GPT prompts. Generation is commoditised; research and verification of the line are not.
The engine
Domains and inboxes, warmup, the sequencer itself, and the other channels.
Inbox & domain infrastructure
The picks-and-shovels layer: dozens of resellers rent Google, Microsoft and private-SMTP mailboxes at $0.50–$5 each so volume senders can spread sends across thousands of inboxes.
Warmup networks
Pools of mailboxes that send, open, rescue and reply to each other to manufacture sender reputation — now bundled free in every volume sequencer and increasingly suspected by the filters.
Sequencing & sending
The sequencer is the most crowded, most commoditised layer in cold email: ~30 credible tools, near-identical features, and per-email prices down to $0.23 per 1,000.
Multichannel: LinkedIn, calls, SMS and video
LinkedIn is the only second channel that matters at scale for cold email buyers, it is the riskiest to automate, and the money has gone to the tool that integrates with sequencers rather than the ones that replaced them.
Outputs
What happens after the send — and the agents trying to do all of it.
Replies, booking and handoff
Everything after the send — unified inbox, reply classification, AI drafting, booking, CRM handoff — is being bundled into sequencers as a credit-metered upsell, while the enterprise routing tools start at $15,000 a year.
AI SDR layer
Agents that run outbound end to end. Buyers signed fast in 2024, cancelled fast in 2025, and in 2026 the survivors sell approvals and human handoff.
Agent mail layer
A new layer of the stack: inboxes, threads and webhooks provisioned by API for software agents. It is cheap and crowding fast, its vendors ban cold outreach on paper, and its customers include AI SDRs that send it anyway.