The Exact Cold Email Tech Stack We Run for 10+ Clients (With Costs)

We run outbound for 10+ clients, and we have dropped more tools than we kept. This is the exact stack, what each piece costs, and why it survived. No affiliate links. Six layers, each depending on the ones below it: skip one and the whole thing breaks.

Data and enrichment

Never rely on one data provider. Every provider has gaps. Chaining multiple providers in a waterfall, cheapest and most likely to hit first, and verifying with BounceBan after each step, closes more of the gap than any single source can on its own.

Cheap SMB lists are mostly covered by Blitz at zero cost; the paid fallbacks handle the more expensive residue. Ordering the waterfall cheapest-first is a real cost lever: querying the expensive providers on everyone, instead of only the leftovers, multiplies your bill for no extra coverage.

• Apollo: fine for account-level firmographics and company research. Kept for that, not for enrichment.
• ZoomInfo: strong org charts, priced for teams bigger than the value it adds us. Dropped.
• Lusha: other providers outperformed it on our ICPs. Dropped.

Research and personalization

Clay is our workflow builder for ICP classification, company research, and personalization variables. Claude powers copy generation: a cheaper model for bulk classification, a stronger model for copy where quality matters more than cost. Good prompts beat model selection. Exa is AI web search for signals a database misses: funding, leadership changes, launches.

Sending infrastructure

3-5 alternate domains per client (.com, .co, .io), never the primary domain. $10-15/domain/year. Google Workspace at roughly $6/mailbox/month, a few mailboxes per domain. Warmup built into the sending platform: 14 days minimum, ideally 21, kept running on all active mailboxes.

We keep sending volume well under the platform's stated ceiling, ramping gradually rather than starting there, and provider matters: Outlook mailboxes need a noticeably lower daily cap than Google Workspace mailboxes to stay clean. Scale by adding domains and mailboxes, never by pushing per-mailbox volume past what the mailbox provider handles well.

Sending platforms

Instantly for teams under a few thousand sends/month. Lemlist when you want email plus LinkedIn plus phone. EmailBison is our primary platform at agency scale, running many campaigns across workspaces. SmartLead was our primary platform before EmailBison; we still run it for one client, but its webhooks don't reliably fire, so we poll instead of depending on them.

CRM and pipeline tracking

We do not dictate CRM; most clients run HubSpot, some Salesforce, a few Attio or Pipedrive. What we own is the layer between campaign platforms and CRM: a system on Supabase we call Lead Ops, tracking every contact, activity, and reply across all platforms. It answers questions like "how many unique contacts have we reached this month" that most teams cannot.

We manage 100+ sending domains across all clients, each client on its own dedicated infrastructure, never shared between clients.

Analytics and monitoring

• Platform-native analytics: reply rates, bounce rates (we never optimize for opens, they're unreliable).
• Supabase dashboards: cross-campaign reporting, dedup, activity timelines.
• Slack alerts: positive replies, bounce warnings, daily health checks.
• Google Postmaster Tools: domain reputation, checked regularly.

Minimum viable stack

Enough to test whether outbound works with a handful of warm addresses and basic data. The gap: Apollo's free tier finds only a fraction of emails; a real waterfall would catch more.

Full agency stack

What not to buy

• All-in-one platforms: do data, sequencing, CRM, and analytics at a B-minus level each. Best-of-breed tools connected through Clay outperform them in our experience.
• AI cold email writers: output is generic and increasingly detectable, by spam filters and by prospects. We use AI for research and first drafts, then have a human review the final send.
• Done-for-you domain packages: a markup on a setup you can build yourself in about 30 minutes per domain.

Picking tools for a new client

1. 01Start with their existing sending platform if it works. No reason to migrate.
2. 02Set up dedicated infrastructure in week one: domains, DNS, mailboxes.
3. 03Connect the enrichment waterfall. Client doesn't need their own data subscriptions.
4. 04Configure monitoring: Slack alerts, Postmaster Tools, health checks.
5. 05Layer in Clay, Exa, and AI enrichment based on how much personalization the campaign needs.

The single most important tool

Email verification, specifically BounceBan. You can recover from bad copy or weak personalization. You cannot recover from a destroyed sender reputation. Every email we send is checked against BounceBan's deliverability verdict before it enters a campaign, not just against a raw score or an unverified "found" status. Skipping verification to save a few dollars on a large list is the fastest way to burn a domain.