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Troubleshoot email delivery

Check authentication, sending reputation and message content when email reaches spam folders.

Updated September 2026

If a sent message lands in spam, check its authentication results and the sending configuration. This guide covers common causes and the details to collect for support.

1. Check email authentication

Start with the authentication results in a test message. A mail testing service can help identify failures; compare them with the records supplied by your email provider.

# Quickly check from command line
dig +short TXT yourdomain.com | grep spf
dig +short TXT default._domainkey.yourdomain.com
dig +short TXT _dmarc.yourdomain.com

# All three should return populated records

2. Check the sending IP for blocklist entries

Check whether a blocklist flags the sending IP. If a listing appears:

  1. For a shared sending IP, email [email protected] with the listing details.
  2. If you're on a dedicated IP, go to each blacklist's removal form and submit a delist request. Include the reason (e.g. compromised account, now fixed).

3. Reverse DNS (PTR) doesn't match

Check the reverse DNS for the sending IP and compare it with the mail server configuration. Contact support if it needs to be changed:

# Find your server's sending IP
dig +short A mail.yourdomain.com

# Check its reverse DNS
dig -x 198.51.100.42 +short

# Should return a name that makes sense, e.g. mail.yourdomain.com
# or server.omdigital.cc : not, say, a random generic hostname

4. Message content triggers filters

Spam filters score content. High-score triggers:

  • All-caps subject lines
  • Subject with lots of punctuation (!!!, $$$)
  • Single-image emails with no text
  • Shortened URLs (bit.ly, tinyurl)
  • Too many links relative to text
  • Words like 'free', 'guarantee', 'congratulations' in the subject

Run the message through mail-tester.com or Mailgun's Postmaster tools. They score content separately from authentication.

5. Domain has no history or a bad history

For a new sending domain, follow your email provider’s guidance on sending volume and monitor delivery results.

Review any history of unwanted sending from the domain and resolve the underlying cause before requesting removal from a blocklist.

6. Recipient has marked earlier mail as spam

If a recipient expected your message but finds it in spam, they can mark it as wanted. For mailing lists, honor unsubscribe requests and review recipients who no longer engage.

A systematic test

  1. Open mail-tester.com in a browser. It shows an address like [email protected].
  2. Send a normal message from your domain to that address.
  3. Wait 30 seconds, then click 'Then check your score'.
  4. Read every item that isn't green. Fix the highest-impact issues first: authentication, then blacklists, then content.
  5. Re-test with a fresh mail-tester address. Repeat until the score is 9/10 or higher.

Common issues

  • Testing a single provider. Compare delivery to mailboxes at more than one provider.
  • Test inbox history. Previous spam decisions can affect subsequent tests.
  • Ignoring DMARC reports. If DMARC shows a pattern of failures, that's your diagnostic. Follow where the failed IPs lead.
  • Website email configuration. Check the sender address and use the authenticated SMTP settings provided by your mail service.

Contact support

Email [email protected] with the test report and recipient domain.

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