Email and DNS guides
Reliable email depends on a handful of DNS records and a few good habits. These guides explain each of them in plain language, with record examples you can adapt for your own domain.
Email authentication and DNS
What is an SPF record and how do you set it up correctly?
SPF syntax explained: include:, ~all vs -all, the 10 DNS lookup limit, why a domain may only have one SPF record, and the mistakes that break it.
DKIM explained: selectors, keys and rotation
How DKIM signatures work, what a selector is, why 2048-bit keys, what the DKIM TXT record looks like and how to rotate a key without breaking mail.
DMARC explained: policies, reports and a safe rollout
DMARC p=none, quarantine and reject, rua and ruf reports, SPF and DKIM alignment, and a step-by-step path to an enforcing policy.
How to add DNS records for email at your registrar
Adding MX, SPF, DKIM and DMARC records step by step, with notes for Cloudflare, OVHcloud, home.pl, nazwa.pl, GoDaddy and Namecheap.
What is an MX record? Priority, backup MX and null MX explained
How MX records route your mail: priority numbers, multiple and backup MX hosts, why MX must point to a hostname, null MX for domains without mail, TTL when switching providers.
Reverse DNS and PTR records for email: what they are and who sets them
What a PTR record is, forward-confirmed reverse DNS, why Gmail and Yahoo require it, IPv6 reverse DNS, and why the IP owner - not your registrar - sets it.
MTA-STS and TLS-RPT: enforcing encrypted delivery to your domain
How MTA-STS (RFC 8461) stops TLS downgrade attacks on incoming mail: the _mta-sts record, the policy file, testing vs enforce, max_age, TLS-RPT reports and DANE.
BIMI: how to show your logo next to your emails
BIMI requirements explained: DMARC at enforcement, an SVG Tiny PS logo, VMC vs CMC certificates, the default._bimi record and which mailbox providers display it.
SPF permerror: how to fix "too many DNS lookups"
SPF's 10-lookup and 2-void-lookup limits (RFC 7208 4.6.4): which mechanisms count, how to count them through nested includes, and safe ways to get back under the limit.
Deliverability: getting mail to the inbox
Why are my emails going to spam?
The usual reasons legitimate mail lands in spam - authentication, reverse DNS, sender reputation, content and unsubscribe handling - and the Gmail and Yahoo sender rules.
Gmail rejecting your emails? Sender requirements and error codes explained
What Gmail and Yahoo require from senders since 2024, and what the 550 5.7.26, 421 4.7.28 and 550 5.7.1 rejections mean and how to fix them.
Outlook rejecting your emails? Microsoft sender rules, NDRs and delisting
Outlook.com's 2025 rules for high-volume senders, what 550 5.7.515 and S3150 blocks mean, SNDS and JMRP, and how to ask Microsoft for delisting.
SMTP bounce codes explained: 4xx vs 5xx and enhanced status codes
SMTP reply codes and enhanced status codes (RFC 5321, RFC 3463), soft vs hard bounces, what a DSN bounce report contains and what to do per code.
Email blacklists: how to check, why you got listed and how to get removed
How DNS blocklists like Spamhaus and Barracuda work, how to check your IP and domain, why listings happen and how delisting works, also on shared IPs.
How to warm up a new domain and IP address for email
Why a new domain or IP has no reputation, how to ramp up volume gradually, why engagement and list hygiene matter, and what to watch in Postmaster Tools.
Email for your business
How to get email on your own domain (you@yourcompany.com)
Buying a domain, choosing a mail host, publishing MX, SPF, DKIM and DMARC, creating inboxes and setting up mail apps - plus typical costs and common pitfalls.
Alternatives to Google Workspace and Microsoft 365 for business email
How to compare business email providers fairly: pricing model, data location and the GDPR, the features you really need, calendars and documents, and leaving again.
How to switch email providers without losing mail
Lower the TTL, set up the new provider first, copy old mail over IMAP or with imapsync, switch the MX record, keep the old account for a while - with a checklist.
Shared inboxes for teams: running support@ and office@ together
Forwarding, shared passwords, shared mailboxes and helpdesk tools compared - plus assignments, internal notes and permissions, and how shared inboxes work in AnyMail.
Business email security basics: phishing, spoofing and hijacked accounts
Phishing, spoofing, lookalike domains and invoice fraud (BEC), and the defences that work: DMARC enforcement, two-factor sign-in, app passwords and an incident plan.
Mail apps and developers
IMAP and SMTP settings: set up email in Thunderbird, Outlook, Apple Mail, iPhone and Android
Server names, ports 993 and 587, SSL/TLS vs STARTTLS, usernames and app passwords - step by step for every common mail app, plus fixes for certificate and login errors.
IMAP vs POP3: which should you use for your email?
How IMAP synchronises a mailbox and POP3 downloads it, what that means for phones, laptops, folders and offline access, and where SMTP fits in.
How to read email headers to debug delivery problems
Reading the Received chain, Authentication-Results, DKIM-Signature, Return-Path and Message-ID - and how to open the full headers in Gmail, Outlook, Apple Mail and Thunderbird.
Sending email from your application: SMTP, APIs, bounces and webhooks
How to send password resets, receipts and notifications reliably: SMTP or an HTTP API, DKIM on your own domain, safe retries, bounces and event webhooks, with code examples.
Testing email in CI: end-to-end tests for signup and password reset emails
Why mocked mailers miss real bugs, how to wait for a real message in a test, extract the link, keep runs isolated and pick sensible timeouts - and when a local SMTP catcher is enough.