Poor Email List Quality: Using outdated or purchased email lists can lead to higher chances of being flagged as spam. Content Issues: Certain words, phrases, or formats in the email content can trigger spam filters. Lack of Authentication: Failing to implement email authentication protocols like SPF, DKIM, and DMARC can increase the likelihood of being marked as spam. High Complaint Rates: If recipients frequently mark your emails as spam, it can signal to spam filters that your emails are not trustworthy.