---
title: Email API Guides | SendHQ
description: Practical guides for transactional email, deliverability, domain authentication, inbound email, and AI-agent email workflows.
canonical: https://sendhq.cc/guides
last-updated: 2026-08-24
---
# Email API guides for product teams

Clear, implementation-focused answers about transactional email, inbound routing, deliverability, domains, and AI-agent workflows.

- [Amazon SES Cost: A Product Team Pricing Model](https://sendhq.cc/guides/amazon-ses-cost.md): Model Amazon SES cost across recipients, data, pricing plans, dedicated IPs, event infrastructure, quotas, and the engineering layer around delivery. Read page →
- [Amazon SES: What Application Teams Need to Operate](https://sendhq.cc/guides/amazon-ses.md): Understand Amazon SES identities, regions, APIs, quotas, events, suppressions, and the application controls a production email system still needs. Read page →
- [How to Check an SPF Record for Application Email](https://sendhq.cc/guides/check-an-spf-record.md): Check the correct SPF domain, syntax, mechanisms, nested DNS budget, source-IP authorization, result, and DMARC alignment for application email. Read page →
- [How to Check DKIM for Application Email](https://sendhq.cc/guides/check-for-dkim.md): Check DKIM by inspecting a real signature, querying its selector and domain, verifying the message, reading receiver results, and testing alignment. Read page →
- [How to Configure DMARC in Cloudflare Safely](https://sendhq.cc/guides/cloudflare-dmarc.md): Configure Cloudflare DMARC from an audited sender inventory, validate aligned authentication, review reports, and stage policy changes with rollback. Read page →
- [Cloudflare Email Routing: Safe Setup Guide](https://sendhq.cc/guides/cloudflare-email-route.md): Set up Cloudflare Email Routing with verified destinations, explicit rules, bounded Workers, safe MIME handling, observability, and tested rollback. Read page →
- [DKIM Setup Guide for Product Email](https://sendhq.cc/guides/dkim-setup.md): Set up DKIM with owned signing domains, protected private keys, explicit selectors, controlled signing paths, verification tests, rotation, and DMARC alignment. Read page →
- [How to Run a DMARC Check for Application Email](https://sendhq.cc/guides/dmarc-check.md): Check DMARC record discovery, syntax, SPF and DKIM alignment, policy, reports, and real application messages without confusing a DNS lookup with delivery. Read page →
- [Email API Implementation Guide for Product Teams](https://sendhq.cc/guides/email-api.md): Design a safe email API integration with verified domains, queued sends, stable identifiers, controlled retries, delivery events, suppression, and tenant isolation. Read page →
- [Email Bounce-Back Troubleshooting for Product Teams](https://sendhq.cc/guides/email-bounce-back.md): Handle email bounce-backs by preserving SMTP and DSN evidence, separating temporary from permanent failures, suppressing unsafe retries, and reconciling outcomes. Read page →
- [How to Evaluate an Email Deliverability Service](https://sendhq.cc/guides/email-deliverability-service.md): Evaluate email deliverability services by scope, evidence, authentication, feedback loops, suppressions, privacy, portability, and operational fit. Read page →
- [How to Evaluate an Email Validation Service](https://sendhq.cc/guides/email-validation-service.md): Evaluate email validation services by syntax, DNS, SMTP evidence, uncertainty, privacy, freshness, consent boundaries, APIs, and operational fit. Read page →
- [How to Evaluate a Free SMTP Service](https://sendhq.cc/guides/free-smtp-service.md): Evaluate free SMTP services by real workload limits, expiry and overage terms, TLS and authentication, domain setup, events, suppressions, support, and exit cost. Read page →
- [Gmail API Implementation Guide for Product Teams](https://sendhq.cc/guides/gmail-api.md): Implement Gmail API access with least-privilege OAuth, durable mailbox sync, safe sending, bounded retries, and a clear service-account model. Read page →
- [Google SMTP Relay Service Evaluation Guide](https://sendhq.cc/guides/google-smtp-relay-service.md): Evaluate Google Workspace SMTP relay by authorization model, TLS, sender identity, quotas, error handling, authentication, observability, and migration risk. Read page →
- [Mailgun API Implementation Guide for Product Teams](https://sendhq.cc/guides/mail-gun-api.md): Implement Mailgun with verified domains, scoped credentials, durable send jobs, authenticated webhooks, precise events, and suppression-aware workflows. Read page →
- [SMTP Mail Protocol: How Application Email Moves](https://sendhq.cc/guides/mail-protocol-smtp.md): Learn how SMTP submission, relay, envelopes, response codes, TLS, retries, and message content shape an application email workflow. Read page →
- [Office 365 SMTP Details for Applications](https://sendhq.cc/guides/office-365-smtp-details.md): Understand Microsoft 365 SMTP client submission, connector relay, Direct Send, OAuth, TLS, hosts, ports, identities, limits, and application tradeoffs. Read page →
- [Postmark API Implementation Guide for Product Teams](https://sendhq.cc/guides/postmark-api.md): Implement Postmark with server-scoped tokens, verified senders, durable jobs, explicit message streams, exact API outcomes, secure webhooks, and suppressions. Read page →
- [Python 3 SMTP: Safe Production Implementation](https://sendhq.cc/guides/python3-smtp.md): Implement Python SMTP with EmailMessage, verified TLS, server-only secrets, explicit envelopes, durable jobs, partial-recipient handling, and bounded retries. Read page →
- [Resend Email API Implementation Guide for Product Teams](https://sendhq.cc/guides/resend-email-api.md): Implement the Resend email API with verified domains, scoped keys, idempotent sends, signed webhooks, durable events, and honest delivery states. Read page →
- [SendGrid API Implementation Guide for Product Teams](https://sendhq.cc/guides/sendgrid-api.md): Implement SendGrid with authenticated domains, scoped API keys, durable send records, verified event webhooks, and suppression-aware workflows. Read page →
- [SMTP Ports 25, 465, and 587: A Practical Guide](https://sendhq.cc/guides/smtp-port.md): Choose the right SMTP port by role and TLS mode, then diagnose connection, handshake, authentication, and message acceptance failures. Read page →
- [Safe SMTP Email Sending with Python](https://sendhq.cc/guides/smtp-python.md): Implement Python SMTP sending with durable jobs, EmailMessage, authenticated TLS, bounded timeouts, exact recipient outcomes, and evidence-driven retry handling. Read page →
- [How to Evaluate an SMTP Relay Service](https://sendhq.cc/guides/smtp-relay-service.md): Evaluate SMTP relay services by submission security, authentication, queues, retry behavior, limits, delivery events, suppression, isolation, and migration fit. Read page →
- [SPF Record Syntax Explained for Application Email](https://sendhq.cc/guides/spf-record-syntax.md): Understand SPF v=spf1 syntax, mechanisms, qualifiers, modifiers, DNS lookup limits, include and redirect behavior, validation, and DMARC alignment. Read page →
- [Yahoo Mail Authentication Failed: Diagnostic Guide](https://sendhq.cc/guides/yahoo-mail-authentication-failed.md): Diagnose Yahoo authentication failures by preserving SMTP evidence, separating temporary and permanent replies, and testing SPF, DKIM, DMARC, and alignment. Read page →
- [Email API: Send, Receive, and Track Transactional Email](https://sendhq.cc/guides/email-api.md): Understand what an email API does, how sending and inbound receiving work, and what to evaluate before choosing one. Read guide →
- [Transactional Email API Guide](https://sendhq.cc/guides/transactional-email-api.md): A practical guide to sending passwords, receipts, alerts, and other product-triggered email reliably. Read guide →
- [How to Send Email with an API](https://sendhq.cc/guides/send-email-with-api.md): A step-by-step approach to authenticated API email sending, testing, and production safety. Read guide →
- [How to Receive Email with an API](https://sendhq.cc/guides/receive-email-with-api.md): Route inbound mail to your application, parse it safely, and make it useful in a product workflow. Read guide →
- [Email Domain Verification: SPF, DKIM, and DMARC](https://sendhq.cc/guides/email-domain-verification.md): What domain verification is, why it matters, and how SPF, DKIM, and DMARC work together. Read guide →
- [Improve Email Deliverability: Issues, Factors, and Monitoring](https://sendhq.cc/guides/email-deliverability.md): How to improve email deliverability: the factors that decide inbox placement, common deliverability problems, and how to monitor delivery rates. Read guide →
- [Inbound Email Webhooks: Design Patterns and Safety](https://sendhq.cc/guides/inbound-email-webhooks.md): Use webhooks to process inbound messages without building a polling mailbox workflow. Read guide →
- [Email API for AI Agents](https://sendhq.cc/guides/email-api-for-ai-agents.md): Give agents a constrained, observable way to send and receive product email without exposing mailbox credentials. Read guide →
- [Amazon SES API: A Practical Integration Guide](https://sendhq.cc/guides/amazon-ses-api.md): Use Amazon SES for application email while keeping your provider layer, domains, and observability under your control. Read guide →
- [Resend Alternative: What to Compare](https://sendhq.cc/guides/resend-alternative.md): A neutral checklist for comparing developer-focused email platforms without migrating blindly. Read guide →
- [KingSMTP Alternative: Monero-Payable Email API with MCP](https://sendhq.cc/guides/kingsmtp-alternative.md): Compare SendHQ with KingSMTP. Both accept Monero; SendHQ adds an MCP server for AI agents, a CLI, OpenAPI 3.1, inbound inboxes, and hosted templates. Read guide →
- [Maileroo Alternative: Email API with MCP, Payable in Monero](https://sendhq.cc/guides/maileroo-alternative.md): Compare SendHQ with Maileroo. Both take crypto; SendHQ also takes Monero and adds an MCP server for AI agents, a CLI, and an OpenAPI 3.1 contract. Read guide →
- [Email API with Node.js](https://sendhq.cc/guides/email-api-nodejs.md): A server-side pattern for sending transactional email from Node.js without leaking API keys. Read guide →
- [Email API with Python](https://sendhq.cc/guides/email-api-python.md): A backend-safe pattern for transactional email from Flask, Django, FastAPI, or a worker. Read guide →
- [Email Bounce Handling for Product Teams](https://sendhq.cc/guides/email-bounce-handling.md): Classify bounces, suppress unsafe recipients, and keep critical product email observable. Read guide →
- [SPF, DKIM, and DMARC Explained](https://sendhq.cc/guides/email-dkim-spf-dmarc.md): A plain-language explanation of the DNS records that establish email authentication and alignment. Read guide →
- [Transactional Email vs Marketing Email](https://sendhq.cc/guides/transactional-email-vs-marketing.md): Understand the different consent, content, and reputation requirements for product messages and campaigns. Read guide →
- [How to Evaluate Email API Pricing](https://sendhq.cc/guides/email-api-pricing.md): Compare email API pricing by capabilities and operational fit, not only by messages per month. Read guide →

## Competitor reviews

Sourced summaries of what users say about other providers.

- [Resend reviews](https://sendhq.cc/reviews/resend.md)
- [SendGrid reviews](https://sendhq.cc/reviews/sendgrid.md)
- [Mailgun reviews](https://sendhq.cc/reviews/mailgun.md)
- [Postmark reviews](https://sendhq.cc/reviews/postmark.md)
- [Amazon SES reviews](https://sendhq.cc/reviews/amazon-ses.md)
- [Brevo reviews](https://sendhq.cc/reviews/brevo.md)
- [AgentMail reviews](https://sendhq.cc/reviews/agentmail.md)
- [MailerSend reviews](https://sendhq.cc/reviews/mailersend.md)
- [Mailtrap reviews](https://sendhq.cc/reviews/mailtrap.md)
- [SparkPost reviews](https://sendhq.cc/reviews/sparkpost.md)