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Security Insights · sh.consulting

Why Emails Land in Spam: 9 Causes and How to Fix Them

· Original article ↗

Summary

Based on 100+ audits, SH Consulting identifies nine causes of spam-folder placement, including weak sender reputation, unengaged lists, broken authentication, spoofing and overmailing, with monitoring and configuration steps to improve deliverability and protect domains

Key points

  • A high delivery rate means messages were accepted, not that they reached inboxes; mailbox filters use reputation and engagement signals to determine placement.
  • Complaints, bounces, low engagement, spam traps and overmailing can damage domain or IP reputation; shared infrastructure can expose other senders to the effects.
  • The article recommends checking SPF, DKIM and DMARC across every sending domain, and reviewing DMARC reports before moving from p=none toward an enforcement policy.
  • DMARC reporting can help identify unauthorized senders; spoofed messages may carry phishing links, password-reset scams or malicious attachments.
  • The article describes how attackers could abuse customizable SaaS notification flows to send phishing emails through a platform's trusted domain.
  • Suggested steps include monitoring Google Postmaster Tools, suppressing persistently unengaged recipients, and controlling sending volume and frequency.

Article Details

Topic
Email deliverability problems, domain and IP reputation, authentication, and abuse of shared SaaS email infrastructure

Vendors

Googlefactor in inbox placement decisions at Gmail, and it carries significant weight with other providers too. Google Postmaster Tools rates your domain on a four-tier scale: High, Medium, Low, and Bad. If your domain dropsMicrosoftIP reputation matters most at Microsoft, which relies heavily on it for spam filtering decisions. But it's a factor everywhere. Your IP reputation is the aggregate result of every message sent from that IP address — theSendGridbe more aggressive — don't mail them more than two or three times before suppressing. If you're on SendGrid, use the Engagement Quality (SEQ) Score API to monitor engagement health across subusers on a daily

Products

Google Postmaster Toolsinbox placement decisions at Gmail, and it carries significant weight with other providers too. Google Postmaster Tools rates your domain on a four-tier scale: High, Medium, Low, and Bad. If your domain drops belowGoogle Workspaceso you can't set up SPF, DKIM or DMARC for it. Move to your own domain on a paid mailbox such as Google Workspace, configure authentication properly, then raise volume gradually while you watch Postmaster Tools,Sender ScoreHow to fix it: Check your IP reputation across multiple sources: Google Postmaster Tools, Sender Score, and Talos Intelligence. They don't always agree, and you need the complete picture. If you're on shared IPs andSendGridbe more aggressive — don't mail them more than two or three times before suppressing. If you're on SendGrid, use the Engagement Quality (SEQ) Score API to monitor engagement health across subusers on a dailyTalos Intelligenceit: Check your IP reputation across multiple sources: Google Postmaster Tools, Sender Score, and Talos Intelligence. They don't always agree, and you need the complete picture. If you're on shared IPs and sending

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