Transactional Email and APIs
These are developer-facing APIs and SMTP relays for the mail your app sends on its own, password resets, receipts, shipping updates, one-time codes, not the campaigns a marketer schedules by hand. Pricing runs by email volume rather than list size, and the real differentiator is deliverability engineering, not template design.
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Twilio's email API, and the highest-volume transactional sender most developers will have already touched without noticing, since it powers mail for a huge share of SaaS products. It ships both a raw send API and a separate contact-based marketing tool, billed on two different meters under one account.
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Zoho's transactional email service with SMTP relay and REST API, designed for transactional-only sending.
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A transactional-only email API built by Wildbit and now owned by ActiveCampaign, known for treating deliverability as the whole product rather than a feature. It keeps transactional mail on separate infrastructure from bulk sends, and its logs let you see exactly what happened to a specific message within minutes of sending it.
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All-in-one marketing platform with dedicated transactional email API and 300 free emails per day.
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Mandrill API for application-triggered emails, now integrated into Mailchimp with SMTP and HTTP options for developers.
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Customer data platform with transactional email API for password resets, receipts, and system notifications
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Cloud-based email delivery platform built on advanced MTA technology with API and SMTP options for transactional messages.
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A newer email API built by the team behind the open source React Email project, aimed squarely at developers already working in React and Next.js. The dashboard, SDKs, and template system feel closer to a modern developer tool than a legacy ESP retrofitted with an API.
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A developer-first email API that came out of Y Combinator in 2011 and has stayed close to that audience through several changes of ownership, now under Sinch. Inbound routing rules let you parse and act on replies programmatically, a feature many transactional APIs skip entirely.
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SMTP relay and email API with global server network and real-time monitoring for transactional message delivery.
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A French email platform, founded in Nantes in 2010, that pairs a transactional API with a drag-and-drop campaign editor built for real-time collaboration between several people editing the same email at once. It sits under the same parent company as Mailgun but runs as its own separate product with its own pricing and dashboard.
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Multi-channel platform offering transactional email via SMTP and API with up to 12,000 free monthly emails.
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Multi-channel notification API routing transactional messages across email, SMS, push, and chat from a single integration.
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A budget-focused email API and SMTP relay started in 2010 by engineers in Vancouver and Szczecin, Poland, aimed at senders who care more about the per-email rate than a polished interface. It covers both transactional API sends and basic marketing campaigns from the same account.
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Enterprise-grade SMTP relay and API service with reputation management and advanced routing controls.
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Transactional email platform with separate send and bulk streams, REST API and SMTP relay for developers.
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A smaller, Pennsylvania-based transactional email provider running since 2007, built around giving even lower-volume customers their own IP reputation rather than pooling everyone onto shared infrastructure. Its InboxReady reporting tracks placement and reputation metrics that some larger providers reserve for their top-tier plans.
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Developer-focused transactional email API from MailerLite with templates, webhooks, and real-time delivery analytics.
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AWS's raw email sending service, priced at ten cents per thousand emails with no subscription of any kind, the cheapest way to move real volume if you're comfortable wiring it up yourself. There's no template editor or contact management to speak of, just an API and SMTP endpoint that plug into the rest of AWS.
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Lightweight transactional email API and SMTP focused on simplicity, starting at $5/month for 1,000 emails.
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Privacy-focused EU-hosted transactional email API with fast delivery and minimal tracking by default.
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SaaS email platform combining marketing and transactional email with free transactional sends on paid plans
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Transactional email API for AI agents with MCP server, templates, flows, and multi-provider support
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Transactional email API with AI-driven inbox placement optimization for reliable delivery to end user inboxes.
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Open-source self-hostable transactional email platform with API and SMTP relay, built on AWS SES.
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AI-driven email platform that connects to Postgres and Supabase to trigger transactional emails with natural language
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Open source self-hosted mail server for sending and receiving email, positioned as an alternative to hosted transactional services.