The software is not where the money goes. Running 1,000 inboxes costs well under $200 a month in compute on your own stack (my estimate below), and an LLM reply classifier costs a fraction of a cent per reply. The expensive lines are engineers who understand mail protocols, an annual Google security assessment, SOC 2 if you sell upmarket, and deliverability support — the human work of telling customers why their inboxes landed in spam.
The single most expensive mistake is buying the mailbox layer from a per-account email API. At Nylas's $2.00 per connected account or Unipile's $3.50–5.50 (October 2026), 1,000 inboxes cost $2,000–5,500 a month — while Instantly sells unlimited inboxes from $37.60 a month (annual Growth plan, October 2026). Build the connectors yourself.
Salary figures are assumptions, not sourced data: a fully loaded cost of €90k–130k a year per experienced engineer in Germany. Replace them with your own. Headcount for "parity" is my judgement from incumbents' estimated team sizes, not a disclosed figure.
Benchmarks: what the incumbents employ
| Company | Team size | Revenue | Source |
|---|---|---|---|
| Instantly | ~200 employees (Jan 2026); 15 full-time in 2022 | $38.2M ARR (2026, estimate); $2.4M (2022) | GetLatka, estimates |
| Smartlead | 93 employees (June 2024) | $14M ARR (2024, estimate) | GetLatka, estimate |
Instantly reached a reported 2,900 paying customers with a 15-person team in 2022 (GetLatka, same page). That is the real benchmark for an MVP-stage company: a small team can carry thousands of customers if the product is self-serve and deliverability support is systematised.
Neither company discloses its engineering-versus-support split. The ~200 Instantly figure includes sales, support and its lead-database and CRM teams.
Stage 1: MVP (months 0–6)
Scope (see MVP spec): app-password IMAP/SMTP and Microsoft Graph connectors, scheduler with per-inbox caps and rotation, campaigns with steps and variants, CSV lead import, unified inbox, reply/bounce/OOO detection, open/click tracking with custom domains, basic analytics, billing, public API and webhooks. No owned warmup network, no lead database, no owned infrastructure.
| Role | Count | Why |
|---|---|---|
| Founder / product | 1 | Customer interviews, deliverability knowledge, copy |
| Backend: mail protocols and scheduler | 1–2 | IMAP, SMTP, Graph, MIME, threading, idempotency |
| Full-stack: app and unibox | 1 | Campaign builder, inbox UI, billing |
| Deliverability / support (part-time from month 4) | 0.5 | First customers need hand-holding |
People cost (assumption above): 3 engineers × 6 months ≈ €135k–195k. Add Google verification and a CASA assessment if you ship Google OAuth (see below), and around €1k–3k a month in cloud, tooling and domains (my estimate).
Stage 2: Instantly parity (years 1–3)
"Parity" means roughly the 2026 Instantly surface: sequencer, unibox, warmup network, a B2B lead database, CRM, AI reply and campaign tools, done-for-you inboxes, placement tests and multi-workspace agency accounts. See the feature matrix for the full list and Instantly for its product.
| Team | Engineers (my estimate) | Owns |
|---|---|---|
| Sending engine | 4–6 | Connectors, scheduler, ingestion, quotas |
| Deliverability & warmup | 3–5 | Warmup network, health scoring, placement tests, infra partners |
| App & unibox | 4–6 | Campaign builder, inbox, analytics, workspaces |
| Data | 3–6 | Lead database, enrichment, verification (Contact data and enrichment, Email verification) |
| AI | 2–4 | Personalisation, reply agent, campaign builder |
| Platform & security | 2–4 | Multi-tenancy, SOC 2, CASA, SSO, API |
| Total | ~20–35 |
At the assumed €90k–130k loaded cost, 20–35 engineers is €1.8M–4.5M a year before support, sales and marketing. Parity is a Series A-sized programme — or several years of profitable bootstrapping, as Instantly did. That is the argument for picking a wedge instead.
Infrastructure cost per 1,000 inboxes
My estimate for running your own connectors, at 30 sends per inbox per day (about 900k emails a month):
| Component | Load at 1,000 inboxes | Estimated monthly cost |
|---|---|---|
| IMAP/Graph/Gmail workers | 1,000 long-lived connections or push subscriptions | A small share of one VM |
| Send workers | ~30k sends/day | Negligible |
| Postgres (messages, events) | Few million rows/month | Tens of dollars at this size |
| Tracking edge + TLS for custom domains | Few hundred domains | Tens of dollars |
| Total | Roughly $50–200 (estimate) |
Compare buying the layer:
| Option | Price (October 2026) | Cost per 1,000 inboxes/month |
|---|---|---|
| Nylas Pro | $2.00 per connected account | ~$2,000 |
| Unipile | $4.50 per account (201–1,000 tier) | ~$4,500 |
| EmailEngine (self-hosted, source-available) | $1,450 / €1,200 per year, unlimited mailboxes | ~$120 + your servers |
EmailEngine is the only "buy" option compatible with unlimited-inbox pricing; it handles IMAP, SMTP, Gmail API and Graph behind one REST API. Its vendor says one instance carries "several thousand" mailboxes before you shard. For an MVP it can save 2–3 months of connector work; at 100k inboxes you will want your own code.
LLM costs
At Claude API list prices (October 2026: Haiku 4.5 $1/$5 per million input/output tokens; Sonnet 5.5 $2/$10; Batch API 50% off), my arithmetic:
| Task | Tokens (in/out) | Model | Cost per unit | Per 100k units |
|---|---|---|---|---|
| Reply intent classification | 800 / 20 | Haiku 4.5 | ~$0.0009 | ~$90 |
| First-line personalisation | 1,500 / 150 | Haiku 4.5 | ~$0.0023 | ~$225 |
| Same, higher quality | 1,500 / 150 | Sonnet 5.5 | ~$0.0045 | ~$450 |
| Same, batched overnight | 1,500 / 150 | Sonnet 5.5 batch | ~$0.0023 | ~$225 |
Personalising every email of a 100k-email month costs a few hundred dollars. Web research per lead (fetching and summarising a company site) multiplies input tokens 5–10×; that is where AI SDR products spend. See AI personalisation, AI reply agent and The AI shift.
Compliance
| Item | Cost | Frequency | Needed when |
|---|---|---|---|
| Google CASA (restricted Gmail scopes) | $540–720 (TAC Security, per Nango) to $3,000–6,000 (Leviathan AL1 list, Leviathan) | Annual | Google OAuth beyond 100 users |
| Microsoft publisher verification | Free | Once | Multitenant Graph app |
| SOC 2 Type 2 | Audit $10k–50k; all-in first year $10k–80k+ (Vanta, compliance-software vendor) | Annual | Selling to SDR teams and enterprise (In-house SDR teams, Enterprise RevOps buyers) |
| GDPR (DPA, records of processing, EU hosting) | Mostly legal time | Ongoing | From the first EU customer (GDPR and ePrivacy) |
Engineering time is the hidden cost: CASA evidence and SOC 2 controls each consume engineer-weeks per year.
Support
Cold email support is deliverability consulting: DNS records, warmup, bounce spikes, spam placement. It does not shrink with a better UI. Instantly's 2022 ratio — 2,900 paying customers on a 15-person team (GetLatka) — suggests a self-serve product can run at one person per ~200 customers early on, with heavy reliance on docs, community and templated deliverability checks.
No incumbent discloses support headcount, ticket volume per customer or cost to serve. Treat support load as the most uncertain line in this budget.
What this means for an entrant
- Do not chase parity. It is a 20–35 engineer, multi-year programme (my estimate). Ship a wedge with 3–4 engineers in 4–6 months (The wedge, The first 90 days).
- Build the connector layer yourself, or license EmailEngine for the MVP. Per-account email APIs cost $2–5.50 per inbox per month and make unlimited-inbox pricing impossible.
- Infrastructure and LLM costs are rounding errors next to salaries; do not let them drive pricing. Margin lives in people efficiency (see Unit economics, Pricing strategy).
- Put CASA ($0.5k–6k/yr) in year one and SOC 2 ($10k–80k+) only when you go after SDR teams. Agencies and founders do not ask for SOC 2.
- Hire for mail-protocol and deliverability expertise first. It is the scarcest skill and the one that decides retention.