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The most common causes: (1) SPF, DKIM, or DMARC not configured or misaligned; (2) Gmail or Microsoft scoring your domain or IP poorly; (3) complaint rate above 0.1%; (4) blacklist listings; (5) low recipient engagement; (6) content patterns that spam filters flag. Brain's Deliverability DNA scan finds the exact cause for your specific domain in under 60 seconds. Run a free scan →

When one provider files you as spam and the other doesn't, it is almost always how Gmail scores your domain. Gmail's spam filter leans heavily on your domain's history and on how each recipient treats your mail. Check Google Postmaster Tools for your domain reputation score. Brain's Radar Monitor spots the split between providers in real time, and RCA Inspector works out the Gmail-specific cause automatically.

A sudden move to spam is almost always caused by: (1) a complaint-rate spike above 0.1% from a high-volume send or bad list segment; (2) a new blacklist listing; (3) an SPF or DKIM change (adding a new ESP without updating SPF); or (4) a volume spike on a new or under-warmed domain. Brain's alert system sees the signal that moved within minutes; RCA Inspector traces the exact cause.

Cold email lands in spam for a few usual reasons: sending from your primary domain instead of a dedicated sending domain, an under-warmed domain, missing or misconfigured SPF, DKIM or DMARC, sending volumes above safe limits for your domain age, or content patterns that spam filters flag. See the complete cold email inbox playbook →

DMARC (Domain-based Message Authentication, Reporting & Conformance) is a DNS record that tells mailbox providers what to do when an email fails SPF or DKIM. Since 2024, Google and Yahoo require DMARC for all bulk senders. Even for low-volume senders, a missing DMARC record makes it much more likely your mail lands in spam. Set up DMARC at minimum p=none with rua= reporting enabled. Complete DMARC setup guide →

SPF lists which servers are authorised to send email from your domain. DKIM adds a cryptographic signature proving the message wasn't altered in transit. DMARC ties SPF and DKIM together — it specifies what mailbox providers should do when emails fail those checks, and requires that the domain that passed aligns with your visible From: address. All three are required for reliable inbox delivery.

This is an alignment failure. DMARC requires that the domain in your SPF or DKIM result aligns with your visible From: domain. If you send from yourcompany.com but route through an ESP that signs with the ESP's own domain in DKIM, alignment fails even though DKIM itself passes. Fix: configure a custom sending domain in your ESP so DKIM signs with your domain. Brain's RCA Inspector specifically diagnoses alignment failures.

SPF, DKIM and DMARC prove you are who you say you are. They do not guarantee inbox placement. The most common causes: Gmail or Microsoft scoring your domain or IP poorly, a shared IP with bad senders, low recipient engagement, content patterns that spam filters flag, or inconsistent sending volume. Full diagnostic guide →

Brain's Domain Health module checks your domain and sending IPs against every major blacklist in real time and alerts you within minutes of any new listing. For a free one-time check, use MXToolbox's blacklist checker. Complete blacklist removal guide →

Step 1: Find out why you were listed using Brain's RCA Inspector. Step 2: Fix the cause completely (stop the spam flow, remove bad list segments, secure compromised accounts). Step 3: Submit a removal request to the blacklist operator. Step 4: Watch for removal and inbox-rate recovery in Brain's Radar Monitor. Never submit a removal request before fixing the cause — you'll be relisted immediately.

Brain's Radar Monitor tracks where your email actually lands, in real time, separately for Gmail, Yahoo, Outlook, and Apple Mail. It also alerts you when your inbox rate at one provider drops while the others stay stable. What is inbox placement? → · Connect your ESP, no card →

95%+ is a strong inbox rate across all major providers. 90%+ at Gmail is considered good (Gmail is the most demanding). Overall inbox rates below 85% mean a lot of your mail is in spam and you need a diagnosis. See benchmarks by provider → · Inbox placement vs deliverability →

A seed test uses seed lists — monitored email accounts across Gmail, Outlook, Yahoo, and other providers. You send to these seeds, and the tool reports where each email landed: inbox, spam, promotions, or missing. Complete testing guide →

Brain watches all your sending domains at once, catches spam-rate spikes and domain-score drops in real time, tracks inbox rates per provider, and tells you why when a problem shows up. Complete cold email playbook → · How to choose a deliverability tool →

For a properly warmed domain (after 4-6 weeks of warmup), 200-500 emails per day is a safe operational volume. For higher volumes, use multiple dedicated sending domains. The critical metric is not volume but complaint rate — keep it below 0.08% at all times. Brain watches complaint rates in real time across all your sending domains.