Email Reputation

Email reputation determines whether your messages reach inboxes or disappear into spam folders. But here's what most guides won't tell you: reputation isn't really about following rules. It's about being wanted.

Every metric that email providers track—authentication, complaints, bounces, engagement—is asking the same question: Do people want to hear from this sender? Get that right, and the technical details fall into place. Get it wrong, and no amount of perfect configuration will save you.

The Two Reputations

Email providers track reputation at two levels, and you need both.

IP reputation follows the sending server. It tracks volume, bounce rates, complaint rates, and authentication. Think of it as the reputation of the post office that sends your mail.

Domain reputation follows your From address. It tracks how people interact with messages from your domain—do they open them, click links, reply? Or do they delete without reading, mark as spam, never engage?

Modern systems weight domain reputation heavily. This matters because you can change IPs, but your domain follows you. Burn your domain reputation and you're starting from scratch with a new identity.

What Providers Actually Measure

The algorithms are proprietary, but the signals are knowable:

Authentication compliance. Do your messages pass SPF, DKIM, and DMARC? Consistent authentication builds trust. Failures—even occasional ones—erode it. Providers see failed authentication the way you'd see a letter with a forged return address.

User engagement. This is where reputation gets interesting. Providers watch whether recipients open messages, click links, reply, save them, spend time reading—or delete without opening, mark as spam, never interact. You can do everything technically right and still land in spam because nobody opens your emails. Technical correctness doesn't save you from being ignored.

Complaint rates. When someone clicks "Report Spam," that's a vote against you. Even small increases matter. Above 0.1% is a warning sign. Above 0.3% is a problem. Above 1% is a crisis.

Bounce rates. Sending to addresses that don't exist signals poor list hygiene. Hard bounces (invalid addresses) hurt immediately. Sustained bounce rates above 5% indicate you're not maintaining your lists.

Sending patterns. Consistent senders look legitimate. Sudden spikes, erratic schedules, and long gaps look suspicious. Spammers send in bursts then disappear. Legitimate senders show up regularly.

The Warm-Up Problem

New IPs and domains start with no reputation—which is almost as bad as bad reputation. Providers are suspicious of unknown senders, and rightfully so.

The solution is warm-up: gradually increasing volume so providers can observe your behavior and build trust. Start with 50-100 emails per day. Double every few days. Watch your metrics. Adjust based on what you see.

Critically: during warm-up, send to your most engaged users first. These are people who will open, click, and reply—proving to providers that you're wanted. Sending to your coldest list segments during warm-up is self-sabotage.

How Reputation Dies

Reputation builds slowly and dies fast.

Spam traps are email addresses that should never receive mail. Some are pristine—addresses that were never valid, created specifically to catch spammers scraping the web. Some are recycled—old addresses that bounced for years, then were reactivated as traps. Hitting either damages reputation, but pristine traps are worse. They prove you're not getting permission.

Blacklists are shared databases of known bad senders. Getting listed on Spamhaus, SpamCop, or Barracuda affects deliverability across thousands of mail servers. Removal requires fixing the underlying problem and requesting delisting—a process that takes days to weeks.

Sudden volume spikes look like a compromised account or a purchased list. Even if legitimate, they trigger scrutiny.

Content that looks like spam can hurt reputation even with perfect authentication. Excessive images, suspicious links, patterns that match known spam—all contribute.

Monitoring What Matters

Google Postmaster Tools shows your reputation with Gmail, authentication rates, spam rates, and encryption usage. Gmail is often the largest portion of any email list. If you're not monitoring Postmaster Tools, you're flying blind.

Microsoft SNDS (Smart Network Data Services) provides similar data for Outlook.com and Office 365. Register your sending IPs to see how Microsoft views you.

DMARC aggregate reports show authentication results across all providers. They tell you what percentage of your mail is passing SPF and DKIM, and from which IPs.

Blacklist monitoring catches listings before they cascade into delivery failures. MXToolbox and MultiRBL offer free checking. Set up alerts rather than checking manually.

Shared vs. Dedicated IPs

With shared IPs, you inherit whatever reputation the IP already has—good or bad. Other senders' behavior affects you. But you don't need warm-up, and the provider manages reputation. This works for lower volumes (under 100K emails per month) if you trust your provider.

With dedicated IPs, your reputation is yours alone. Bad neighbors can't hurt you, but you start with nothing and must warm up. This makes sense at higher volumes, but requires active management. You can't just set it and forget it.

Large senders often use IP pools—separate dedicated IPs for transactional email versus marketing. If marketing generates complaints, transactional email (password resets, order confirmations) stays unaffected.

The Subdomain Strategy

Some organizations separate sending by subdomain:

• mail.example.com for corporate communication
• newsletter.example.com for marketing
• alerts.example.com for transactional messages

This provides reputation isolation. If marketing reputation suffers, critical transactional email can still deliver.

But use this strategically, not evasively. Constantly rotating subdomains is a spam tactic. Providers recognize it.

When Reputation Fails

If reputation deteriorates, the response depends on severity.

For minor issues—slight delivery decline, small reputation dip—clean your list, improve targeting, and monitor closely. Recovery takes one to two weeks.

For moderate damage—significant spam folder placement, elevated complaints—stop sending to unengaged users entirely. Send only to people who've opened in the last 30 days. Fix any authentication issues. Request blacklist removal if listed. Recovery takes one to two months.

For severe damage—most mail blocked, critical blacklistings—you may need to stop sending entirely while you clean house. Remove all bounces, all complainers, all inactive addresses. Consider requiring existing subscribers to re-confirm (re-permissioning). Rebuild slowly. Recovery takes three to six months.

For catastrophic damage—complete blocking, multiple major blacklistings, domain burned—new infrastructure may be the only option. New IPs, potentially new domain. Starting over.

The Core Truth

Email reputation systems exist because email has no built-in trust. Anyone can send from any address. Spam is easy and cheap. So providers built systems to answer the only question that matters: Should we deliver this?

They answer it by watching what you do and how people respond. Perfect authentication proves you are who you say you are. Low complaints prove you're not annoying people. High engagement proves you're wanted.

Reputation isn't a score to game. It's the answer to whether you deserve to reach someone's inbox. Build something people want to receive, and reputation follows.