Even strong campaigns can hit the spam folder if they trigger filters. Inbox providers (Gmail, Outlook, Yahoo) constantly evaluate your domain, IP, and content. If enough risk signals stack up, messages are filtered.
Common reasons emails go to spam:
Untrusted domain or IP: New, un-warmed domains/IPs, or ones with a poor reputation, are more likely to be filtered.
Missing or failing authentication: SPF, DKIM, or DMARC not set up—or failing—reduces trust and can trigger spam placement.
Weak list hygiene: Old or purchased lists, spam traps, typos, role addresses (info@, sales@), and high bounce rates harm reputation.
Low or negative engagement: Consistently low opens/clicks, high deletes-without-reading, and spam complaints teach filters to down-rank your mail.
Content red flags: Spammy phrases, misleading subjects, excessive punctuation/ALL CAPS, too many images vs. text, or suspicious/shortened public links.
Missing required elements: No visible unsubscribe link or physical mailing address violates laws and increases spam filtering.
Sending patterns and spikes: Sudden volume jumps, bursty sends, or inconsistent cadence look risky to filters.
Problematic links and attachments: Linking to blacklisted domains, broken redirects, or attaching executable files/compressed archives can trigger blocks.
Technical/format issues: Broken HTML, no plain-text part, huge images, odd encodings, or mismatched From/Reply-To.
For best practices on improving deliverability and inbox placement, check out this help center article.