Do words like 'viagra' trigger spam filters in email subject lines?

Key findings

• Context matters: ESPs analyze the overall context of an email, not just isolated words, to determine its legitimacy.
• Sophisticated filtering: Modern spam filters use a complex scoring system involving hundreds of factors.
• Reputation is key: Sender reputation is a primary factor in deliverability, often outweighing content keywords.
• Not a single word trigger: A single word rarely causes an email to go to spam on its own; it's part of a larger assessment.
• Older filters: Some older or less sophisticated filters (e.g., small, niche ISPs) might still be more sensitive to specific keywords or less common blocklists.

Key considerations

• Maintain good sender reputation: Focus on overall email practices to build and maintain a strong sender reputation, which is crucial for getting into the inbox.
• Audience engagement: Sending to an engaged, opt-in list significantly reduces spam complaints and improves deliverability, as filters learn from recipient interaction.
• Holistic approach: Understand that deliverability is affected by many factors beyond content, including IP/domain health and authentication. Our guide on why your emails go to spam provides more detail.
• Avoid tricky character usage: Do not use unusual spacing (e.g., V I A G R A) or special characters (e.g., Vi@gr@) to mask words, as this is a clear spam indicator and can actually hurt your deliverability. According to Textmagic, such tactics are counterproductive.

Key opinions

• Historical concern: Many marketers recall a time when certain words were immediate spam triggers, leading to an enduring cautious mindset.
• Contextual understanding: Some believe modern filters are intelligent enough to differentiate between legitimate and illicit usage of words like viagra.
• A/B testing for safety: Marketers frequently suggest A/B testing subject lines containing potentially risky words to assess their actual impact on deliverability and engagement.
• Recipient behavior: Even if an email bypasses automated filters, certain words might increase the likelihood of recipients manually marking it as spam, negatively impacting sender reputation.
• Bad reputation amplification: For senders with an already weak reputation, including 'risky' words can compound existing deliverability issues, leading to more emails landing in the spam folder or being placed on a blacklist or blocklist.

Key considerations

• Evaluate your audience: Consider how your specific audience might react to sensitive words in your subject lines, as their perception can influence engagement and spam complaints.
• Monitor engagement: Pay close attention to open rates and spam complaint rates when using potentially risky terms, as these metrics provide direct feedback on content acceptance.
• Prioritize positive sending habits: Focus on list hygiene, relevant content, and proper authentication over rigid word avoidance. According to Mailjet, avoiding certain words is just one piece of the puzzle.
• Small list limitations: A/B testing on very small segments might not yield statistically significant results, making it difficult to draw firm conclusions about word impact.

Key opinions

• Myth debunking: Experts frequently emphasize that single 'trigger words' alone do not dictate spam placement in modern filtering systems.
• Holistic evaluation: Spam filters examine hundreds of factors, not just individual words, to assess an email's legitimacy.
• Distinguishing intent: Large providers can differentiate between legitimate discussions (e.g., a study about viagra) and actual spam (e.g., a fraudulent sale of counterfeit drugs).
• Reputation is paramount: A strong sender reputation is far more influential than the presence of certain words, as outlined in our guide on domain reputation.
• Older systems: Smaller, less advanced ISPs might still employ cruder keyword-based filtering, but these are less common for professional accounts.

Key considerations

• Focus on overall hygiene: Good sending practices, including list quality and infrastructure, are far more important than adhering to a spam word list.
• Sender domain and IP reputation: These are crucial indicators for mailbox providers and should be regularly monitored.
• Email authentication: Proper SPF, DKIM, and DMARC implementation builds trust and signals legitimacy to receiving servers. Our guide to email authentication explains more.
• Contextual analysis: Rely on the intelligence of modern filters to understand the true nature of your content. Don't self-censor legitimate discussion.
• Avoid deliberate obfuscation: Deliberately misspelling or altering words to bypass filters can actually hurt deliverability, as it mimics known spammer tactics. As Word to the Wise explains, filters are more sophisticated.

Key findings

• Rule-based systems: Spam filters like SpamAssassin use a variety of rules, some of which assign scores based on keyword presence, including terms like viagra. (As referenced by SpamAssassin documentation).
• Scoring system: Emails accumulate points from various rules; a high cumulative score, not a single rule, results in spam classification.
• Keyword weighting: Keywords might contribute to a spam score but typically don't trigger a block on their own; their weight is determined by broader patterns of abuse.
• Authentication importance: Documentation heavily emphasizes the role of protocols like SPF, DKIM, and DMARC in email validation and preventing spoofing.
• No exhaustive list: There's no definitive, universal list of 'spam words' provided by major mailbox providers, as their filtering logic is proprietary and constantly evolving.

Key considerations

• Understand scoring: Recognize that a word might add a small score to an email, but it's part of a much larger equation where multiple factors contribute to the final spam decision.
• Regular rule updates: Spam filter rules are constantly updated to combat new spamming techniques, meaning a static list of 'trigger words' quickly becomes obsolete.
• Beyond content: Technical configurations and sender behavior are often more critical than content for documentation and actual filter performance, as explained in Microsoft's spam classification insights.
• Abuse patterns: Documentation often focuses on identifying broader patterns of abuse and deceptive practices rather than just individual words or phrases.