04 What the products actually do · 22 pages · 16k words
Features
Twenty-two features, each with how it works, who does it well, where implementations differ, and whether it is table-stakes or a place to win. The matrix at the bottom shows twelve products side by side.
Sending
How mail is spread, limited, varied, tested and branched.
Inbox rotation
One campaign spread across many sending mailboxes so each stays under a safe daily cap. Every serious tool has it; the differences are in scale, assignment logic and pricing gates.
Sending limits and throttling
Per-mailbox daily caps, campaign caps, ramps and send gaps: the controls that keep volume under what Google and Microsoft tolerate. Vendors converge on ~30/day per cold mailbox.
Spintax and message variants
Randomised text so no two emails in a campaign are byte-identical. Universal in volume tools, syntax differs, and it is being overtaken by AI-written per-lead copy.
A/B testing
Split leads across copy variants and pick a winner. Variant counts range from 2 (lemlist) to 26 (Instantly); none of the leaders documents statistical significance.
Conditional sequences and subsequences
Branching on what a lead did (replied, clicked, accepted on LinkedIn) or what they said. Volume tools bolt on 'subsequences'; lemlist has the richest branching; reply-intent routing is the frontier.
Multichannel steps
LinkedIn, call, SMS and WhatsApp steps inside the email sequence. Native in lemlist, Reply.io, Saleshandy and the suites; bolted on or absent in the volume sequencers.
Deliverability
The features that decide whether mail reaches the inbox.
Built-in warmup
Peer-to-peer networks that exchange, open and reply to fake emails to build mailbox reputation. Bundled free by every volume tool; pool quality is now the upsell.
ESP matching
Send to Gmail recipients from Google mailboxes and to Outlook recipients from Microsoft mailboxes. Common in volume tools since 2024; stops at Google/Microsoft/Zoho and its impact numbers are unaudited.
Bounce protection
Auto-pausing sending when bounces cross a threshold. Every leader has a campaign-level version with different maths; mailbox-level, rolling-window protection is rare.
Inbox placement testing
Seed-list tests that show whether a mailbox lands in inbox or spam at Gmail and Microsoft. Increasingly built in, often as a paid add-on, and structurally blind to real-recipient filtering.
Custom tracking domains
Your own CNAME for open-pixel and click-redirect links instead of the vendor's shared domain. Universal, cheap, and increasingly paired with turning tracking off altogether.
Workflow
Replies, CRM, data, verification and reporting.
Unified inbox (Unibox)
One inbox for replies across hundreds of sending mailboxes. Universal, rarely differentiated, and the surface where AI reply handling now lives.
CRM sync
Pushing replies, interested leads and activity into HubSpot, Salesforce or Pipedrive. Plan-gated or add-on at the volume tools; native at the suites.
Built-in lead database
Contact data sold inside the sequencer on credits. Every volume tool now has one; it is a revenue line, not a moat.
Built-in email verification
Checking addresses before sending to keep bounces under 1–2%. Increasingly free or bundled; a commodity being given away.
Campaign analytics
Sends, opens, replies, positive replies and meetings by campaign, step and mailbox. Universal and shallow; the gap is outcome and deliverability attribution.
AI
Personalisation, reply agents, campaign builders.
AI personalisation
LLM-written first lines and full emails per lead, billed in credits. Everyone ships it; nobody has published proof it lifts replies.
AI reply agent
An LLM that classifies, drafts and sends responses to inbound replies, with or without human approval. Instantly meters it per reply; the rest are uneven.
AI campaign builder
Describe the target and offer; the AI picks leads, writes the sequence and launches. Shipping as in-app agents and, increasingly, as MCP tools inside Claude and ChatGPT.
Platform
White-label, API, workspaces — what agencies and builders need.
White-label and agency portals
Rebranding the sequencer so agencies can give clients a login under their own name. Priced per client at Smartlead and Woodpecker, plan-gated at Instantly, structural at EmailBison.
API, webhooks and MCP
Programmatic control of campaigns, leads and replies, event webhooks, and — new in 2026 — official MCP servers for AI agents. Completeness varies more than marketing suggests.
Workspaces, roles and SSO
Separating clients or teams into workspaces, controlling who can do what, and the enterprise controls (SSO, audit logs) that procurement asks for. Strong at the suites, thin at the volume tools.
The matrix
Twenty-two features across twelve products, compiled from vendor help centres and docs in October 2026. "Unknown" means the docs did not say — not that the feature is missing.
yes partial / plan-gated$ paid add-on no? not establishedHover a cell for the note. Sources are on each feature page.