Learn
Guides to transactional email that actually arrives
Deliverability, authentication, sending infrastructure, and implementation — written for the engineers who own the mail their product cannot afford to lose.
- 10 in-depth guides
- Current sender requirements
- Infrastructure, not just API calls
Start here
The foundation
If you read one thing, read this. Everything else in the library builds on it.
Pillar guide · 14 min read
Transactional email: the complete guide for developers
Transactional email is the mail your product sends because a user did something — a receipt, a password reset, a security alert. It is the only category of email where a single missed message becomes a support ticket. This guide covers what it is, how delivery actually works, and what mailbox providers require of you now.
Read the guide →- What counts as transactional email
- What actually happens between your API call and the inbox
- The sender requirements you must meet in 2026
- How to structure transactional sending in your application
- Measuring transactional email properly
3 guides
Foundations
What transactional email is, how it differs from marketing mail, and how to evaluate a provider.
Transactional email: the complete guide for developers
What transactional email is, how it differs from marketing mail, the delivery path from API call to inbox, and the sender rules enforced in 2026.
14 min read
Transactional vs marketing email: why you must separate the streams
How transactional and marketing email differ, why mailbox providers score them as one sender by default, and the subdomain and IP architecture that separates them.
12 min read
How to choose a transactional email service
A buyer’s guide to transactional email providers: the three architectural models, the questions that actually predict deliverability, and where pricing hides.
13 min read
3 guides
Deliverability
Authentication, sender requirements, bounce handling, and the signals mailbox providers actually score.
Email deliverability: the 2026 playbook for transactional senders
The sender requirements Gmail, Yahoo, and Microsoft enforce, the signals they score, how to diagnose a placement problem, and how to recover from a reputation hit.
16 min read
SPF, DKIM, and DMARC explained (with the alignment rule everyone misses)
How SPF, DKIM, and DMARC actually work, the record syntax, the alignment rule that breaks otherwise-correct setups, and a safe rollout from p=none to p=reject.
16 min read
Email bounces, complaints, and suppression: a handling guide
Hard vs soft bounces, how to read SMTP status codes, what belongs on a suppression list, and the architecture that keeps a bad address from damaging your reputation.
14 min read
3 guides
Sending infrastructure
Shared pools, dedicated IPs, warmup, and the build-versus-buy decision for your own mail servers.
Dedicated IP vs shared IP: choosing your sending infrastructure
When a dedicated IP helps and when it hurts, the volume you need to keep one warm, what providers actually mean by "dedicated," and the questions to ask about a shared pool.
13 min read
IP warmup: how to bring a new sending IP to full volume
Why new sending IPs need warming, a realistic 4–6 week ramp schedule, the rules that prevent a stall, and how domain warmup differs from IP warmup.
12 min read
Email infrastructure: what it takes to run your own, and when to
The full stack behind outbound email, what running your own mail servers actually costs, why sending IPs are hard to acquire and keep clean, and when it is worth it.
13 min read
1 guide
Implementation
Patterns for the messages your product cannot afford to lose.
Why we write these
Deliverability is an infrastructure problem
Most email advice stops at "set up SPF and DKIM." That is necessary and nowhere near sufficient. The part nobody writes about is who else sends from the IP addresses carrying your mail.
Pool
Paying only
transactional traffic, no free tier
Marketing on it
Never
no campaigns, no cold outbound
Dedicated
Warmed by us
your own servers and IPs
API
Unchanged
same contract at every tier
We own and operate the infrastructure our customers send from, which is why these guides can be specific about pool composition, warmup, and IP identity instead of vague. If a guide makes a claim about how we run things, ask us to show you.
Put the guides into practice
Verify a domain, create an API key, and send your first transactional email in about ten minutes. Sandbox is free; production runs on a transactional-only network.