Diagnose email authentication and alignment from a real message
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.
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Posts tagged deliverability
Browse email infrastructure articles tagged deliverability.
DKIM selector not found: diagnose and repair
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.
DMARC quarantine vs reject — what to pick at each ramp stage
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.
A practical IP warming schedule you can hand to a new customer
A practical guide to PulsePigeon's staged dedicated-IP volume caps, reputation thresholds, minimum dwell, and safe pauses when a gate is not met.
How we automated dedicated-IP warm-up without overloading reputation
An engineering writeup of PulsePigeon's dedicated-IP warm-up automation: per-IP stage state, reputation gates, bounded evaluation, and fail-closed rollout controls.
SMTP 421 — transient failure retry strategy
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.
SMTP 550 — permanent failure codes and what to do with each
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.
SMTP relay, explained — and why free public relays are not safe for production
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.
SPF too many DNS lookups: diagnose and fix the limit
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.
Warming up a new sending domain without losing deliverability
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.