STOP YOUR
EMAILS
GETTING FLAGGED
Free tools to diagnose why your emails land in spam. Check content, blacklists, and DNS authentication — no account required.
THREE TOOLS.
ONE MISSION.
Everything you need to diagnose and fix your email deliverability — before your customers never see your message.
Spam Score Checker
Paste your subject and body. We analyze 500+ spam triggers and score your content before it hits the inbox.
Run checkBlacklist Checker
Check your domain or IP against 28+ major email blacklists simultaneously. Find out if you're blocked before you send.
Run checkDNS Validator
Validate your SPF, DKIM, and DMARC records. Misconfigured DNS is the #1 cause of emails landing in spam.
Run checkEMAIL DELIVERABILITY EXPLAINED
Email deliverability is the ability of your emails to successfully reach recipients' inboxes rather than landing in spam or being blocked entirely.
Modern spam filters at Gmail, Outlook, Yahoo, and Apple Mail use hundreds of signals to decide where your message lands. These signals fall into three categories: content quality, sender reputation, and DNS authentication. MailFlagger checks all three for free.
Roughly 1 in 6 legitimate emails never reaches the inbox. For transactional emails — password resets, receipts, notifications — a deliverability failure is a direct business problem.
Why Emails Go to Spam
- // Spam trigger words — Content like "FREE", "GUARANTEED", "ACT NOW" activates Bayesian spam filters trained on billions of known spam messages.
- // Domain or IP blacklisting — If your sending domain or IP appears on a DNSBL, receiving servers automatically reject or defer your mail.
- // Missing SPF record — Without a valid Sender Policy Framework record, receiving servers cannot verify your sending IP is authorized.
- // No DKIM signature — DomainKeys Identified Mail provides a cryptographic signature that proves your email wasn't tampered with in transit.
- // Weak DMARC policy — A DMARC record with p=none provides no protection. Use p=quarantine or p=reject to protect your domain.
- // High bounce rates — Sending to stale addresses signals poor list hygiene and damages your sender reputation over time.
COMMON QUESTIONS
Everything developers, marketers, and business owners ask about email deliverability — answered directly.
- Why are my emails going to spam even though they look legitimate?
- Spam filters score hundreds of signals simultaneously — content patterns, sender reputation, authentication records, and engagement history. A perfectly written email still fails if your SPF record is missing or your sending IP appears on Spamhaus. Use all three MailFlagger tools to diagnose each layer independently.
- What's the difference between a spam filter and a blacklist?
- A spam filter evaluates your email content — words, formatting, links. A blacklist (DNSBL) is an external database that flags your sending domain or IP as a known spam source. You can pass every content check and still get blocked if your IP is listed on Spamhaus or Barracuda.
- Do I need SPF, DKIM, and DMARC — or just one?
- You need all three, and they work together. SPF alone can be bypassed via the From header. DKIM alone doesn't stop domain spoofing. DMARC ties them together — but only works if SPF or DKIM is already in place. Gmail and Yahoo now require all three for bulk senders.
- Is MailFlagger really free?
- Yes — all three tools are completely free with no account required. Enter your email content, domain, or IP and get results instantly. MailFlagger was built by email developers frustrated with paywalled deliverability tools.
- How long does it take to get removed from an email blacklist?
- Spamhaus offers self-service removal — typically 24–48 hours. Barracuda has a free removal request form. SpamCop listings expire automatically as reports age out. First identify which list flagged you using our Blacklist Checker, then follow that list's delisting process.