Blog
We write about what we learn running our own mail transfer agents: warm-up, reputation, authentication, and the economics of email at scale.
2026-10-20 · 3 min read
A reproducible checklist for comparing SPF, DKIM and DMARC DNS records with the identities in an authorized received email, and for telling authentication from alignment.
2026-10-20 · 4 min read
A tested Python example that verifies a PulsePigeon signed status event, stores a receipt once, rejects a reused event ID with different content, and keeps send idempotency separate from event idempotency.
2026-08-26 · 1 min read
An engineering writeup of PulsePigeon's dedicated-IP warm-up automation: per-IP stage state, reputation gates, bounded evaluation, and fail-closed rollout controls.
2026-08-26 · 1 min read
A practical guide to PulsePigeon's staged dedicated-IP volume caps, reputation thresholds, minimum dwell, and safe pauses when a gate is not met.
2026-08-26 · 2 min read
The SPF 10-lookup limit is one of the most common authentication failures. What causes it, what the error looks like, and the practical fixes that don't break your existing email flow.
2026-08-26 · 2 min read
When a DKIM check fails with 'selector not found', the receiving server could not resolve the public key. Walk through the common causes and the verification steps.
2026-08-26 · 1 min read
How to choose between DMARC policies p=none, p=quarantine, and p=reject as you move a new domain from monitoring into enforcement. The trade-offs and the failure modes.
2026-08-26 · 1 min read
A 550 response means the mailbox rejected the message and is asking you not to retry. Decode the common sub-codes and the right operational response for each.
2026-08-26 · 1 min read
A 421 response is a temporary failure: the receiving server is asking you to retry later. The right retry policy protects your sender reputation and your recipients' patience.
2026-08-26 · 2 min read
A server-only Next.js REST example for order receipts, with stable idempotency, accepted message IDs, error handling, and delivery-event follow-up.
2026-08-26 · 1 min read
Conceptual guidance for server-side sends from FastAPI, including idempotency, response handling, and when a durable worker is safer than BackgroundTasks.
2026-08-26 · 1 min read
Wire a PulsePigeon send into a Node.js HTTP handler or a BullMQ worker. Idempotency keys, error handling, and a typed error model.
2026-08-26 · 1 min read
The Python SDK pattern: synchronous and asynchronous clients, deterministic idempotency keys, status-specific errors, and application-owned retries.
2026-08-26 · 1 min read
What an SMTP relay does, how it differs from a transactional email API, and why the free public SMTP relays that come up in search results are a reputation risk you cannot afford.
2026-08-26 · 1 min read
A disclosed, criteria-based guide to evaluating Resend, Mailgun, SendGrid, Amazon SES, and PulsePigeon for transactional email.
2026-08-26 · 1 min read
A criteria-based guide to evaluating Mailchimp, Kit, Brevo, Mailgun, SendGrid, and PulsePigeon for campaigns and broadcasts.
2026-08-26 · 1 min read
A repeatable integration checklist for evaluating email APIs: request contracts, error handling, retries, signed events, and release verification.
2026-08-26 · 1 min read
A practical provider-evaluation worksheet for developer-heavy teams comparing Resend, Mailgun, SendGrid, Amazon SES, and PulsePigeon.
2026-08-26 · 1 min read
A SaaS-focused framework for comparing Mailgun, SendGrid, Customer.io, and PulsePigeon without unsupported rankings.
2026-08-26 · 1 min read
A startup-oriented framework for comparing Resend, Mailgun, SendGrid, Amazon SES, and PulsePigeon by evidence, cost, and operational load.
2026-08-26 · 1 min read
A consolidated decision framework for comparing email service providers across developer, SaaS, startup, transactional, and campaign needs.
2026-07-28 · 1 min read
How to use idempotency keys when sending transactional email so retries after a timeout never result in a duplicate message reaching a customer.
2026-07-14 · 1 min read
A practical warm-up schedule for a new sending domain: volume ramps, engagement signals, and the authentication records to land in the inbox instead of spam.