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Building an AI agent · Guide 2 of 6

How to build an AI SDR: full architecture of automated outbound

Building an AI SDR is 80% infrastructure and 20% prompts. The visible part — generated copy, sequences — is the easy one. The part that decides whether it works — domains, warmup, deliverability, lead enrichment, scoring — is the one almost nobody wants to build and the one that almost always fails.

Full architecture (diagram)

A serious AI SDR architecture has five layers, with two-way flow between most of them:

  1. Data layer — sources (Apollo, Clay, LinkedIn) feeding the system.
  2. Scoring layer — model that weights and prioritizes leads.
  3. Copy layer — LLM with a system prompt + per-lead enriched data.
  4. Sending layer — Instantly, Smartlead or equivalent with warm-up and rotation.
  5. CRM layerHubSpot/Pipedrive/Salesforce with two-way sync.

Domains and email infrastructure (SPF, DKIM, DMARC, warm-up)

The piece that decides whether your email hits the inbox or spam. Without this dialed in, none of the rest matters.

  • Secondary domains. Never use your primary domain for outbound. Buy 1-5 secondary domains (acme.io, getacme.com, etc.).
  • SPF, DKIM, DMARC configured correctly from day one. Without them, you're spam by default.
  • 2-3 week warm-up ramping volume gradually from a new domain.
  • Reasonable per-inbox volume — 50-150 emails/day max. More is gambling with your reputation.
  • Reputation monitoring with GlockApps, MailReach or similar.

Lead sourcing and enrichment

Prompt quality is directly proportional to data quality. The standard tools in 2026:

ToolStrengthApprox. cost
ApolloVolume, broad B2B data$50-300/mo depending on use
ClayAdvanced enrichment with waterfalls$150-800/mo
ZoomInfoEnterprise quality$8,000-30,000/year
LinkedIn Sales NavNative LinkedIn data$70-150/mo per user
ClearbitEnrichment by domain or email$500-2,000/mo

Scoring and triggers

Not every lead is worth the same. Scoring decides who to prioritize and when to reach out:

  • Static scoring — based on firmographics (title, company, industry).
  • Dynamic scoring — based on signals (site visit, whitepaper download, role change).
  • Triggers — events that fire specific sequences (new funding, key-role hiring, press mention).

Sequences with AI personalization

A well-designed sequence has 3-7 touchpoints spread over 2-4 weeks, with AI personalization in at least the first two:

TouchpointDayPersonalization
T1 — Opening emailDay 1High (prospect data + specific angle)
T2 — Value follow-upDay 4-5High (reference to something specific)
T3 — BumpDay 8Low (short reminder)
T4 — Angle shiftDay 12Medium (new angle, similar data)
T5 — FinalDay 18Low (honest breakup)

CRM integration (HubSpot, Pipedrive, Salesforce)

Integration has to be two-way: the agent reads from the CRM (don't contact leads already closed/lost) and writes to it (create contacts, log activity, update fields).

Day-to-day monitoring and deliverability

  • Weekly bounce-rate check (<2% is healthy).
  • Domain reputation monitoring.
  • Reply-rate review by segment and by copy.
  • Monthly prompt and segment iteration based on the data.

Frequently asked questions

SMB volume (50-150 emails/day per domain): 1 secondary domain with 2-3 inboxes. Mid volume (300-1,000 emails/day): 3-5 secondary domains with 8-15 inboxes total. Enterprise (1,000+ /day): architecture per team or segment. Never use your main domain for outbound — that rule is non-negotiable.

SMB setup: €60-120/mo (domains + warmup + inboxes + sending tool). Mid: €200-500/mo. Enterprise: depends on volume, but rarely above €1,500/mo in pure infrastructure. Trap: many "all-in-one" platforms charge €800/mo for what self-hosted costs €150. Read the breakdowns.

To build it, yes — even with Instantly or Smartlead, configuring domains, auth, CRM integration and triggers needs someone technical. To run it, no: once it's built, a commercial or ops profile can iterate copy, segments and sequences without touching code.

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How to build an AI SDR: full architecture of automated outbound · Implementa