Why emails may go to the spam folder
How email spam filters work
Spam filters are systems used by email clients (such as Gmail, Outlook, Yahoo, etc.) to automatically classify incoming messages. These systems use a combination of rules, content scanning, machine learning, email domain/IP reputation scoring, and recipient behavior to decide whether a message is legitimate or unwanted.
Spam filters may be applied at several levels:
- By the recipient’s email client
- By their domain’s server (e.g. Google Workspace, Microsoft 365)
- By external security layers (e.g. firewalls or third-party spam services)
💡 Note: Email providers do not disclose how their spam filters work. Neither Textmagic nor any other email delivery service can see or access specific reasons why a message was flagged as spam. Providers do not share this information, so the filtering criteria are not visible to senders or platforms.
10 common reasons why emails may go to spam
- Missing or incorrect email domain authentication
Emails that are sent from domains without valid SPF, DKIM, or DMARC records are more likely to be flagged as suspicious. These protocols verify that the email was sent from an authorized source. - Domain or infrastructure has a poor reputation
Mailbox providers track reputation across both your sending domain and the infrastructure used to deliver your email. If your domain has a history of spam complaints, high bounce rates, or poor sending practices, it may be flagged. Similarly, the IP address used to send your email can also affect deliverability. - High complaint rates from recipients
If recipients mark your messages as spam or junk, mailbox providers may use this feedback to filter future messages from the same sender. - You don’t keep a clean email list
Sending to invalid or inactive addresses increases bounce rates and spam filtering. Lists should be opt-in, up to date, and regularly cleaned. It is strictly forbidden to send emails to purchased, rented, or third-party contact lists. - Missing or invalid “Reply-To” address
Messages without a working reply address (e.g. [email protected]). are more likely to be flagged. A functioning, monitored reply address improves sender credibility. - Use of short URLs or open redirects
Many spam and phishing messages use shorteners like bit.ly or redirect services. Even legitimate use of these tools can increase spam risk. - Links to untrusted or blacklisted websites
If your message contains links to domains with poor reputations, spam filters may block the entire email. - Spam-like content
Excessive promotional language, all-caps words, misleading subject lines, or unnecessary punctuation (e.g. “!!!”) can trigger content-based filtering. - Poorly formatted HTML or broken design
Emails with malformed HTML, missing alt text, or layout issues may be marked as low-quality or suspicious. - Sudden changes in sending volume
A sudden spike in the number of emails you send — especially from a previously low-volume sender — can be interpreted as suspicious behavior by spam filters. Gradually increasing your sending volume (a process known as warm-up) helps establish a stable sender reputation.
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