Email decision matrix

Use this matrix when picking vendors. Defaults are de-facto standards for Dev-Centr–aligned orgs; alternatives are valid when the job changes.

By job

Job Default Strong alternatives Avoid as default

Inbound to personal Gmail

Cloudflare Email Routing (free)

Google Workspace / Zoho Mail seats

Using a transactional ESP as an inbox

Human outbound via Gmail "Send mail as"

ZeptoMail SMTP + per-user keys; SPF/DKIM in Cloudflare

SMTP2GO; Workspace native SMTP

Resend (keep for app/code only); Brevo free/starter for multi-user; shared "master" SMTP password; Gmail’s own SMTP with custom From under p=reject

App hard transactional

Resend (DX)

ZeptoMail (PAYG + Mail Agents if already standardized); Postmark; SES

Marketing ESP for critical mail; Resend for human Gmail send-as

Product marketing + behavioral journeys

Customer.io (+ Twilio for SMS)

Braze / Klaviyo at scale

Brevo when you need event-driven multi-channel

Classic email marketing (lists/campaigns, little product orchestration)

Brevo / similar ESP

Customer.io (overkill if email-only)

Resend Broadcasts dual-running with another marketing brain

Ultra-cheap high volume, AWS-native

Amazon SES

—

First-week bootstrap for non-AWS teams

Full business inboxes at scale

Google Workspace (or Zoho Mail seats)

—

Forever-managing personal Gmail + SMTP relays for a whole team

Scoring dimensions

Rate providers against:

  • Collaborator seats on cheap tiers — Brevo weak; ZeptoMail / Resend / Customer.io stronger

  • Setup UX — ZeptoMail high; SES low

  • Gmail send-as fit — SMTP credentials + static DKIM; watch IP allowlisting traps (Brevo banner)

  • Product API / SDK DX — Resend high

  • Journey / multi-channel — Customer.io high; Brevo medium as ESP; ZeptoMail none

  • Pricing cliff — ZeptoMail PAYG flat; Resend/CIO have plan steps; Brevo seats

  • Isolation model — ZeptoMail Mail Agents; CIO workspaces; Brevo sub-orgs paywalled

  • IaC maturity — Cloudflare DNS: Pulumi native; ZeptoMail: Dynamic Provider or manual DNS tokens; Brevo: Terraform bridge possible

  • Reputation separation — marketing subdomain vs transactional From

Customer.io vs Brevo

Not a coin flip:

  • Customer.io when the product emits events and you need journeys across email/SMS/push/in-app.

  • Brevo when you mainly need a classic ESP (campaigns/lists/templates), accept collaboration paywalls on cheap tiers, and do not need deep product orchestration.

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