Email Deliverability: How Domain Reputation Matters

## Why Emails Land in Spam When you send an email, the receiving server makes dozens of decisions before delivering the message to the recipient's inbox. These decisions aren't random — they're based on a complex set of signals about the sender's reputation, the email's content, and the domain's history. Understanding these factors lets you proactively build a domain reputation that ensures your legitimate emails reach inboxes. ## What Is Domain Reputation? Domain reputation is a trust score assigned to your domain by email service providers, anti-spam organizations, and commercial reputation services. It reflects the quality of email historically sent from (or claiming to come from) your domain. Unlike IP reputation (which is about the sending server's IP address), domain reputation travels with your domain name regardless of which server or service sends your email. It's why a brand-new domain has poor deliverability even if you're sending from Google's infrastructure. Reputation is not a single score — different providers (Gmail, Microsoft, Yahoo) maintain independent reputation signals, and third-party services like Sender Score, Barracuda, and Spamhaus maintain their own databases. ## The Core Signals ### 1. Email Authentication (SPF, DKIM, DMARC) Authentication is the foundation. Without proper SPF Record, DKIM, and DMARC, your email is immediately suspect. - **SPF Record**: Confirms the sending server is authorized for your domain - **DKIM**: Cryptographically proves the email wasn't altered in transit - **DMARC**: Provides policy enforcement and reporting Gmail, Microsoft, and Yahoo's 2024 sender requirements make all three non-negotiable for bulk senders. Even for low-volume senders, authentication is a basic credibility signal. See SPF, DKIM, DMARC: Email Authentication Trilogy for the complete configuration guide. ### 2. Engagement Metrics Email providers track how recipients interact with your emails: - **Opens**: High open rates signal wanted email - **Clicks**: Engagement confirms recipient interest - **Replies**: Strong positive signal — spam recipients don't reply - **Spam complaints**: The most damaging signal. Even a 0.3% complaint rate puts Gmail senders in danger - **Unsubscribes**: Negative but manageable — better than complaints - **Deletes without opening**: Signals unwanted email These metrics are tracked per sender domain, per recipient domain, and per list/segment. Gmail's Postmaster Tools (free, available to domain owners) shows your spam rate and domain reputation directly. ### 3. Sending Volume and Patterns Sudden volume spikes damage reputation. A domain that sends 10 emails per day jumping to 10,000 overnight looks like a compromised account or spam operation. **Email warming** is the practice of gradually increasing sending volume from a new domain: | Week | Daily Volume | |---|---| | 1 | 50–100 | | 2 | 200–500 | | 3 | 500–1,000 | | 4–6 | 1,000–5,000 | | 7+ | Scale as engagement confirms | Send to your most engaged recipients first (those who previously opened or clicked). High engagement during the warm-up period accelerates reputation building. ### 4. List Quality and Hygiene Sending to invalid, inactive, or purchased email addresses destroys reputation: - **Bounce rate**: High hard bounce rates (permanent delivery failures) signal poor list quality. Keep below 2%. - **Spam traps**: Email addresses maintained by anti-spam organizations specifically to catch bulk senders with poor list hygiene. Hitting spam traps results in immediate blacklisting. - **Unengaged addresses**: Recipients who haven't opened email in 12+ months should be suppressed or re-engagement campaigns run before continued sending. Never purchase email lists. Never scrape addresses from websites. Build lists through explicit opt-in only. ### 5. Sending Infrastructure The Reverse DNS (PTR Record) (PTR record) of your sending server should match its hostname. Receiving servers check that the IP's reverse DNS resolves to a hostname that makes sense for an email server. ``` Sending IP: 203.0.113.1 PTR record: mail.yourdomain.com ← Should match, not "host-203-0-113-1.isp.net" ``` This is primarily an IP reputation factor, but for organizations running their own mail servers (rather than using Google or Microsoft), it matters significantly. ### 6. Domain Age and History Brand-new domains have no reputation — which is treated as a negative signal by some receivers. A domain registered recently and immediately sending email at volume looks like a throwaway spam domain. If you're launching a new domain for legitimate business email, plan for a 4–8 week period of reduced deliverability as reputation builds. Use a professional Email Hosting provider (Google Workspace, Microsoft 365) during this period — their shared infrastructure reputation partially supports new domains while domain-specific reputation accumulates. ## Blacklists: What They Are and How to Get Off Them Email blacklists (also called blocklists or RBLs — Real-time Blackhole Lists) are databases of domains and IPs known to send spam. Receiving servers query these lists before accepting email. ### Major Blacklists - **Spamhaus** (spamhaus.org) — Most widely used; being listed here causes severe delivery problems - **Barracuda Networks** — Used by many corporate mail servers - **SORBS** — Broad coverage, frequently updated - **SpamCop** — User-reported spam database ### Checking Blacklist Status Check your domain at: - mxtoolbox.com/blacklists (checks 100+ blacklists simultaneously) - multirbl.valli.org - spamhaus.org/lookup Blacklist checks examine both your domain name and your sending IP address. ### Getting Delisted If you're on a blacklist: 1. **Identify the cause**: Why were you listed? (Complaints, spam traps, compromised account, bulk sending to unverified lists) 2. **Fix the underlying issue**: Stop sending to bad addresses, review your sending practices, secure any compromised accounts 3. **Request removal**: Most blacklists have a delisting request form. Be honest about what happened and what you've changed. 4. **Wait**: Removal can take 24–72 hours to propagate Spamhaus is the most consequential and the most demanding about evidence of remediation. Provide detailed explanation of the problem and steps taken. ## Google Postmaster Tools Google's free Postmaster Tools dashboard shows: - **Domain reputation**: Low, Medium, High, or Very High - **IP reputation**: For your sending IPs - **Spam rate**: Percentage of your email marked as spam by Gmail users - **Authentication failures**: SPF, DKIM, DMARC pass rates - **Delivery errors**: Why some email failed Set up Postmaster Tools at postmaster.google.com by verifying your domain (via TXT Record or DNS (Domain Name System)-based verification). Check it regularly to catch reputation issues before they become delivery crises. ## Microsoft SNDS and JMRP For deliverability to Outlook.com and Microsoft 365 accounts: - **Smart Network Data Services (SNDS)**: Shows spam complaint rates and spam trap hits for your sending IPs - **Junk Mail Reporting Program (JMRP)**: Gives you copies of complaints from Outlook users Register at sendersupport.olc.protection.outlook.com. ## Handling Spam Complaints A spam complaint happens when a recipient clicks "Mark as spam" in their email client. This is reported back to the sending service via feedback loops. For transactional or marketing email, set up feedback loop processing: - When you receive a complaint, immediately unsubscribe that address - Investigate why the recipient felt the email was spam - Segment your list to find others in similar situations who might complain next Complaint rate below 0.1%: Normal. 0.1%–0.3%: Warning zone, investigate. Above 0.3%: Severe delivery impact incoming. ## Best Practices for Sustainable Deliverability **Send only to people who explicitly signed up**: Double opt-in (where subscribers confirm via a link in a confirmation email) produces better list quality and lower complaint rates than single opt-in. **Make unsubscribing easy**: A clear, one-click unsubscribe reduces complaints. Since 2024, Gmail requires one-click unsubscribe headers in bulk emails. **Send consistently**: Irregular sending patterns (months of silence then a large blast) damage reputation. If your list goes cold, run a re-engagement campaign with smaller volume before resuming full sends. **Segment and personalize**: Relevant email gets engaged with. Irrelevant email gets complained about. Better targeting improves engagement metrics, which improves reputation. **Monitor bounce rates**: Remove hard bounces (permanent failures like invalid addresses) immediately. Sending repeatedly to invalid addresses signals poor list hygiene and gets you blacklisted. **Use a subdomain for bulk sending**: If you send both transactional email (receipts, notifications) and marketing email, use a Subdomain for marketing: ``` Transactional: from [email protected] Marketing: from [email protected] ``` This isolates your primary domain's reputation from your marketing IP reputation. If your marketing campaigns cause spam complaints, they don't damage the reputation of your transactional email. ## New Domain Warming Protocol If you're starting fresh with a new domain for email: Week 1-2: Send only to your most engaged recipients — people who will open and click. Target 50–100/day. All SPF, DKIM, DMARC must be configured before sending the first message. Week 3-4: Expand to full list of recent engagers (opened in last 90 days). Aim for 200–500/day. Monitor bounce rates and complaints daily. Week 5-8: Scale to 1,000–5,000/day as engagement metrics confirm good reputation signals. Watch Postmaster Tools for reputation movement from "Low" to "Medium" or "High." Week 9+: Scale as engagement sustains. A "High" domain reputation in Postmaster Tools means you've built a solid foundation. ## Next Steps - **SPF, DKIM, DMARC: Email Authentication Trilogy** — Authentication is the foundation of reputation - **Domain-Based Email Security Best Practices** — Protect your domain from being used by spammers - **Troubleshooting Email Delivery Issues** — Debug specific delivery failures - **Migrating Email to a New Domain** — Maintain reputation when changing domains