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14 articles in Transactional & SMTP.
Transactional email — receipts, password resets, notifications — runs on different infrastructure and different rules than marketing campaigns. This collection covers the plumbing: SMTP ports and authentication, relays and APIs, error codes and timeouts, dedicated sending domains, and the monitoring that catches delivery problems before your users do. Practical, developer-friendly guides for anyone responsible for email that has to arrive.
Outlook and Microsoft 365 cap sending at roughly 300 to 5,000 recipients a day depending on plan, with about 500 per message. The full Word mail merge walkthrough, why Exchange throttles bulk senders, the compliance gaps around unsubscribes, and when a dedicated bulk email sender is the right move.
Gmail caps bulk sending at roughly 500 recipients a day (about 2,000 on Google Workspace). How BCC, multi-send, and a Google Sheets mail merge compare, why accounts get throttled or suspended, the deliverability handicaps of Gmail blasts, and when a dedicated bulk email sender is the smarter path.
An email API POSTs JSON over HTTPS; SMTP relay runs a multi-step protocol conversation on port 587. This guide compares the two on latency, batching, error handling, templates, and vendor lock-in, includes a full port reference table, and shows the hybrid setup most teams actually end up running.
A shared IP pools your sending reputation with other senders; a dedicated IP gives you an address nobody else uses. This guide compares both across reputation, warmup, volume thresholds, and risk — with a side-by-side table, a realistic warmup schedule, and the deliverability fixes that matter more than either choice.
A practical reference for SMTP error codes: how to read a reply in ten seconds, the difference between 4xx soft bounces and 5xx hard bounces, lookup tables for the codes you will actually hit, and fixes for the five that cause most real-world pain — plus the ports that quietly cause silent failures.
The nine transactional email templates every product needs, with copy examples for password resets, receipts, failed payments, and shipping notices. Includes a transactional vs. marketing comparison table, sending-stream separation advice, variable-naming rules, and a pre-launch QA checklist.
How to choose the best email API in 2026 without getting lost in feature checklists. Covers the eight evaluation criteria that actually predict deliverability, the four categories providers fall into and their tradeoffs, how to read API docs like an engineer, a REST-versus-SMTP comparison table, and a safe migration sequence.
A transactional email is a one-to-one message triggered by a user action. Here is how it differs from marketing email, 16 examples to audit your product against, the SMTP ports and DNS records you need, and where promotional content crosses the line.
SMTP uses ports 25, 465, 587, and 2525. Here's what each port does, how they handle encryption, and which one to use when sending email.
The exact Gmail SMTP settings (smtp.gmail.com, ports 587/465) plus step-by-step instructions to create an App Password and start sending.
SMTP is the internet standard for sending email. This beginner's guide explains what SMTP does, how a message travels, and how it differs from IMAP and POP3.
An SMTP relay forwards your outgoing email through trusted servers so it reaches the inbox. Learn how relays work, how they differ from direct delivery, and when to use one.
How SMTP relay services deliver your email, and the concrete criteria to evaluate one: authentication, IP reputation, own-domain sending, reporting, and pricing.
Transactional emails are triggered by a user's action; marketing emails promote to a list. Here's the difference in purpose, consent, deliverability, and design.