Troubleshooting: Emails Landing in Spam

Introduction

When legitimate email lands in spam, the problem is rarely a single missing DNS record. Mailbox providers combine authentication, reputation, infrastructure signals, message content and recipient behavior to decide placement.

This guide covers the most common causes: SPF, DKIM and DMARC failures or misalignment, blacklisted sending IPs, poor reverse DNS, low domain reputation, spam-like content, high bounce rates, sudden volume spikes, shared hosting reputation issues, and contact forms that spoof the From address.

Quick answer

Why emails land in spam

Spam filtering is probabilistic. A message may pass authentication but still be filtered because the sending IP is listed, the domain is new, recipients rarely engage, or the content resembles bulk abuse.

• SPF, DKIM or DMARC missing, failing or not aligned
• Sending IP or domain on a blacklist
• Missing or generic reverse DNS (PTR)
• Low domain or IP reputation
• Spam-like subject lines, wording or formatting
• Too many links or poor URL reputation
• High hard bounce rate from bad lists
• Sudden large volume from a new sender
• Shared hosting IP with poor neighbor reputation
• Contact forms sending with a spoofed From address
• High complaint rate from recipients marking mail as spam

Why this matters

Fixing spam placement early protects domain reputation and makes later DMARC enforcement safer.

How to check spam causes

1. Run Domain Health Checker on your sending domain.
2. Verify SPF, DKIM and DMARC with the dedicated checkers.
3. Send a test email and inspect Authentication-Results headers.
4. Check the sending IP against Blacklist Checker.
5. Verify reverse DNS with Reverse DNS Checker.
6. Review subject line, links, attachments and HTML formatting.
7. Check recent bounce and complaint rates in your mail provider.
8. Send tests to Gmail, Outlook and Yahoo mailboxes.

Common problems

How to fix

1. Step 1: Check SPF, DKIM and DMARC

   Run the authentication checkers and fix failures before focusing on content or reputation.

2. Step 2: Check blacklists

   Test the sending IP and domain with Blacklist Checker and resolve listings at the source.

3. Step 3: Check rDNS

   Confirm the sending IP has valid PTR that resolves forward back to the same IP.

4. Step 4: Review message headers

   Inspect Authentication-Results, Received timestamps and Return-Path in a test message.

5. Step 5: Review content and links

   Improve subject lines, reduce suspicious links and use consistent branding and unsubscribe options for bulk mail.

6. Step 6: Reduce bounces

   Remove invalid addresses, validate new signups and stop mailing old unengaged lists.

7. Step 7: Avoid sudden volume spikes

   Increase sending volume gradually, especially on new domains, IPs or providers.

8. Step 8: Use authenticated SMTP or transactional email

   Route website and app mail through a reputable SMTP or transactional provider instead of unauthenticated PHP mail.

9. Step 9: Monitor reputation

   Track complaints, bounces, blacklist status and DMARC reports over time.

10. Step 10: Re-test with different mailbox providers

    Send fresh tests to Gmail, Outlook, Yahoo and your own domain mailbox after each fix.

Examples

Authentication-Results: mx.google.com;
  spf=pass smtp.mailfrom=mail.example.com;
  dkim=pass header.d=example.com;
  dmarc=pass header.from=example.com

Received: from mail.example.com (198.51.100.10)
Return-Path: <bounce@example.com>

Frequently asked questions