Email deliverability, end to end
Authenticate your domain, protect your sender reputation, stay out of spam folders, and ship compliant campaigns. Everything you need to actually land in the inbox, organized by topic, written by people who break and fix mail servers for a living.
Email deliverability is the discipline of getting your messages into the recipient’s actual inbox, not the spam folder, not deferred, not silently dropped. It sits at the intersection of DNS, cryptography, sender reputation, ISP filtering rules, and legal compliance. Get one part wrong and your campaign disappears.
The fundamentals haven’t changed in twenty years: prove who you are (SPF, DKIM, DMARC), build a track record over time (IP and domain warmup), respect the recipient (clean lists, easy unsubscribe, no surprises), and watch your signals (bounces, complaints, blocklists, postmaster dashboards). What has changed is the strictness of enforcement. Since Gmail and Yahoo’s February 2024 sender requirements, missing a single piece of authentication or letting your spam-complaint rate drift above 0.3 % can sink an entire program overnight.
This hub is structured around the six areas every sender (solo founder, growth marketer, sysadmin, ESP engineer) has to master. Pick the topic that’s burning today, or work through them in order. Each guide is technical where it needs to be and plain-spoken everywhere else.
Browse by topic
Blocklists
Spamhaus, Barracuda, SORBS and 44 other DNSBLs: checks, delisting, monitoring.
Inbox placement
Gmail tabs, Outlook Focused Inbox, seedlist testing and spam-fold diagnostics.
Editor’s picks
Hand-selected by the SMTPedia team
Frequently asked questions
What is the difference between SPF, DKIM, and DMARC?
SPF (Sender Policy Framework) lists the IP addresses authorized to send mail for your domain. DKIM (DomainKeys Identified Mail) cryptographically signs each message so the recipient can verify it wasn’t altered in transit. DMARC (Domain-based Message Authentication, Reporting and Conformance) ties the two together and tells receivers what to do when a message fails: ignore, quarantine, or reject. All three are TXT records in DNS, and all three are now mandatory for bulk senders to Gmail and Yahoo.
How long does an IP warmup take?
For a dedicated IP, plan on a 30-day ramp from your first send to full daily volume. Start at 50 messages per ISP per day, double every 24 hours if engagement signals (opens, clicks, low complaints) hold, and pause or slow down at the first sign of throttling. Shared IPs need no warmup because the pool is already established, but you still need to warm up your domain reputation, which lives independently of the IP.
Why are my emails going to the Gmail spam folder?
The usual suspects, in order: missing or misconfigured authentication (SPF/DKIM/DMARC), high spam-complaint rate (Gmail’s hard ceiling is 0.3 %), poor list hygiene (bounces, recycled addresses, role accounts), low engagement (no opens or replies on previous sends), spammy content patterns (one-line links, ALL CAPS subject lines, image-only emails), and IP or domain reputation issues. Postmaster Tools surfaces the first five reliably; Mail Tester confirms authentication and content issues for any single send. Our full 12-reason troubleshooting guide covers each cause with a fix.
What is a good bounce rate for cold email?
Under 2 % is healthy. Between 2 % and 5 % is a warning sign, usually a stale or poorly sourced list. Above 5 % and you’re at real risk of being throttled or blocked by major ISPs, regardless of message content. The single biggest lever is pre-send validation: running your list through an email verification service before each campaign typically drops bounce rates by 80 % or more. See our guide on hard vs soft bounces for the full picture.
Do I need a dedicated IP for sending email?
Only if you send consistently (generally at least 50,000 to 100,000 messages per month) and have the engagement metrics to back up the reputation you’ll build. Below that volume, you don’t generate enough traffic for ISPs to form a stable opinion of your IP, and a shared pool from a reputable ESP will outperform a cold dedicated address. Dedicated IPs are a tool for scale, not a status symbol.
How do I check if I’m on an email blocklist?
Run your sending IP and domain against the major DNSBLs: Spamhaus SBL/XBL/PBL, Barracuda BRBL, SpamCop, SORBS, and UCEPROTECT at minimum. Free multi-blocklist scanners like MXToolbox and Spamhaus’s own check tool cover the major DNSBLs in one query. Our email blocklist directory covers 47 DNSBLs with their delisting procedures; act fast because delivery is already degraded.
Looking for help unsubscribing from a service instead of sending mail? Browse our 222 unsubscribe guides →
