Resources
Deliverability, SMTP, security and developer guides, from the people running the infrastructure.
The 2024 Gmail & Yahoo sender rules, explained for developers
Authentication, complaint rates and one-click unsubscribe, what actually changed, and the exact settings that keep transactional mail in the inbox.
Gmail & Yahoo sender rules: what bulk senders must do
Authenticate with SPF and DKIM, publish DMARC, keep complaints under 0.3%, and support one-click unsubscribe.
DeliverabilityDKIM passes but mail still lands in spam — why
Authentication is necessary, not sufficient. Reputation and engagement decide the folder.
DNSThe SPF 10-lookup limit and how to stay under it
Too many include: mechanisms cause a permerror — and a permerror is an SPF failure.
DNSDMARC explained: none, quarantine, reject
DMARC ties SPF and DKIM to your From domain and tells receivers what to do on failure.
DeliverabilityHard vs soft bounces, and why you must suppress hard ones
A hard bounce is permanent. Keep mailing it and you look like a spammer.
ProductMessage streams: keep transactional and broadcast apart
Mixing a marketing blast with password resets lets one bad campaign sink your critical mail.
APIWebhooks done right: verify signatures and deduplicate
Every event is signed and may be retried — verify the HMAC and dedupe on the event id.
DeliverabilityWarming up a new sending IP without getting blocked
Ramp volume gradually so receivers build trust in your pattern.
SMTPWhich SMTP port should you use: 587, 465 or 2525?
587 with STARTTLS is the modern default; 465 is implicit TLS; 2525 is a fallback when others are blocked.
DeliverabilityFive ways to cut your complaint rate below 0.1%
Only mail people who asked, make unsubscribe trivial, and honour it instantly.
SMTPSTARTTLS vs implicit TLS: which port should you use?
A practical guide to 587, 465 and 2525, and why legacy servers sometimes need cleartext auth.
SecurityLocking down API keys with IP allowlists and scopes
Least-privilege keys, per-domain restrictions and rotating credentials without downtime.
Developer GuidesSending your first email with the REST API
From API key to a delivered, DKIM-signed message in under five minutes.
DeliverabilityBounce classification: hard, soft, and what to do about each
How auto-suppression and retries protect your reputation, and when to intervene manually.
Product UpdatesTemplates and Message Streams are here
Reusable copy with variables, and a clean split between transactional and broadcast mail.
Developer GuidesHandling inbound email with routes and webhooks
Forward, store or POST incoming mail to your app, matched by recipient, sender or subject.