Start With a Diagnosis

Before you can fix a deliverability problem, you need to know what’s causing it. “My emails are going to spam” is a symptom, not a cause. The actual problem could be any of a dozen different things — and the fix depends entirely on the cause. Here’s how to systematically diagnose and fix it.

Step 1: Check Your Authentication Records

The first thing to verify is that SPF, DKIM, and DMARC are set up correctly on your sending domain. These are the foundational trust signals that ISPs use to evaluate whether your email is legitimate.

Run your domain through MXToolbox (mxtoolbox.com) and check:

  • SPF record exists and includes all your sending sources
  • DKIM is configured and the signature is passing
  • DMARC policy is published (ideally p=quarantine or p=reject)

If any of these are missing or misconfigured, fix them first. Authentication failures are responsible for a large percentage of inbox placement issues.

Step 2: Check Your IP and Domain Reputation

Your sending IP and domain each have their own reputation score at every major ISP. Check them:

  • Google Postmaster Tools — Shows your domain and IP reputation at Gmail specifically. If either shows “Bad” or “Low”, that’s your problem.
  • Microsoft SNDS — Shows reputation data for IPs sending to Outlook and Hotmail.
  • Cisco Talos — IP reputation used by many enterprise spam filters.
  • MXToolbox Blacklist Check — Checks your IP against 100+ blacklists.

If your IP is on a major blacklist, you need to request delisting and identify what caused the listing (usually: high spam complaints, hitting spam traps, or sending to purchased lists).

Step 3: Review Your Spam Complaint Rate

Google Postmaster Tools shows your spam complaint rate. The scale:

  • Below 0.1% — Good
  • 0.1%–0.3% — Caution zone, investigate
  • Above 0.3% — High: Gmail is actively filtering your mail

High complaint rates almost always trace back to: sending to people who don’t remember opting in, sending too frequently, or making it difficult to unsubscribe. Fix the process, not just the symptoms.

Step 4: Audit Your List Quality

Check your hard bounce rate for the last 5 campaigns. If it’s above 2%, your list has a quality problem. Run the entire list through email verification and suppress all invalid addresses before your next send.

Also look for signs of spam trap hits — if you’re sending to old lists (3+ years) or purchased data, you’re almost certainly hitting recycled spam traps.

Step 5: Check Your Sending Volume Pattern

Sudden spikes in sending volume look like spam to ISPs. If you normally send 10,000 emails per day and suddenly send 500,000, ISPs will throttle or block your mail regardless of your content or reputation.

If you need to scale up volume, do it gradually over several weeks. This is what domain and IP warmup is designed to handle.

Step 6: Test Your Content

Send your email through a spam scoring tool like Mail-Tester (mail-tester.com) or GlockApps. These tools score your email against major filter engines and tell you exactly what’s triggering flags — specific words, HTML issues, image-to-text ratio, missing unsubscribe links, etc.

Step 7: Check the Unsubscribe Experience

Since 2024, Gmail and Yahoo require one-click unsubscribe (RFC 8058) for bulk senders. If you’re not compliant, your mails may be filtered. Also check that your unsubscribe link works — a broken unsubscribe link increases complaints because recipients hit “Report Spam” as a way to stop emails when they can’t unsubscribe.

The Most Common Root Causes

In our experience across thousands of senders, the most common root causes of deliverability problems are:

  1. Missing or broken DKIM/SPF/DMARC (accounts for ~40% of cases)
  2. High spam complaint rate from sending to unengaged or purchased lists (~30%)
  3. IP on a blocklist due to sending to spam traps (~15%)
  4. No IP/domain warmup before scaling volume (~10%)
  5. Content or HTML issues triggering content filters (~5%)

Work through the steps above in order and you’ll identify the problem. If you’re still stuck, our deliverability team can review your setup. Contact us.