What words and practices should be avoided in email subject lines?

Key findings

• Outdated advice: Many traditional 'spam word' lists are largely irrelevant today. Filters have evolved beyond simple keyword matching, focusing more on contextual cues and sender behavior.
• Sender reputation is key: A strong sender reputation is paramount. Even if a subject line contains a word often considered 'spammy,' a sender with good reputation and engagement is less likely to be blocked.
• Engagement matters: High open rates, clicks, and replies signal to inbox providers that your emails are valued, overriding minor subject line infractions. Conversely, low engagement or complaints are strong negative signals.
• Authentication protocols: Proper implementation of email authentication standards, such as SPF, DKIM, and DMARC, builds trust with mailbox providers, giving legitimate emails a better chance of inbox delivery regardless of subject line content.
• Recipient behavior: If recipients mark your emails as spam, regardless of the subject line, it will negatively impact your deliverability. Focus on providing value to your audience.

Key considerations

• Contextual relevance: A word like 'free' might be fine if your email is genuinely about a free offer and your sending practices are solid, but problematic if it's used deceptively.
• Mobile optimization: Keep subject lines concise and clear, as they are often truncated on mobile devices. Long, verbose subject lines are a poor practice.
• Avoid deceptive practices: Do not mislead recipients with your subject line. This can lead to complaints and harm your sender reputation, which is far more impactful than a 'spam word'.
• Punctuation and capitalization: Excessive exclamation points (e.g., !!!) and ALL CAPS are more likely to annoy recipients and prompt spam complaints than to trigger a filter directly. However, they can still be a signal for filters, especially if combined with other poor practices. Mailchimp recommends limiting punctuation to three marks per subject line for best practices.
• Focus on value: Craft subject lines that clearly communicate the email's value to the recipient. This encourages opens and engagement, which are the real drivers of deliverability.
• Test and adapt: Regularly test your subject lines and monitor your inbox placement to understand what works for your specific audience and sending patterns. Tools like the ActiveCampaign blog often provide updated advice on avoiding spam triggers.

Key opinions

• The 'spam word' myth: Many marketers question the direct impact of individual 'spam words' like 'FREE' or '!!!' on deliverability today, suggesting this advice is largely outdated folklore rather than a current rule.
• Focus on reputation: There's a growing consensus that sender reputation and positive recipient interaction are far more critical than isolated words in subject lines.
• Avoidance of misleading practices: Regardless of specific words, deceptive or misleading subject lines are universally considered poor practice because they lead to negative user experiences and complaints.
• Punctuation and capitalization: While not always direct spam triggers, marketers agree that excessive punctuation or all caps can make an email appear unprofessional or 'shouty,' leading to negative recipient perception.

Key considerations

• User experience focus: Marketers should prioritize creating subject lines that are clear, concise, and provide value to the recipient, encouraging organic engagement rather than relying on gimmicks.
• Outdated advice persistence: Be cautious of old advice that may no longer apply to modern spam filtering. What was true a decade ago regarding spam trigger words might not be relevant today.
• Brand perception: Even if a word doesn't trigger a spam filter, its use might align your brand with less reputable senders in the eyes of the recipient.
• Testing is vital: A/B testing subject lines provides real-world data on what resonates with your audience and performs well, which is more reliable than generic lists. The EverString blog highlights top words to avoid.

Key opinions

• Context over keywords: Experts emphasize that email filters evaluate the entire context of an email, including sender history and recipient engagement, rather than just isolated keywords in the subject line. This means that a word like 'free' used legitimately is unlikely to trigger a filter on its own.
• Sender reputation reigns: The primary determinant of inbox placement is the sender's reputation (IP and domain). A high reputation can allow for more flexibility in subject line content.
• User engagement is critical: Positive engagement metrics (opens, clicks, replies) strongly signal to mailbox providers that the email is desired. Negative signals (spam complaints, deletions without opening) are far more damaging than any subject line word.
• Authentication is foundational: Robust email authentication (SPF, DKIM, DMARC) is essential for proving sender legitimacy and building trust with inbox providers.
• Misleading practices: Any subject line that is deceptive or misleading, regardless of specific 'spam words,' is universally condemned by experts as it directly leads to user complaints and poor sender reputation.

Key considerations

• Don't fear 'spam words' excessively: While extreme usage of all caps or excessive punctuation can still be a red flag, experts advise against paralyzing fear over specific keywords. Focus instead on providing genuine value.
• Build strong sender reputation: Prioritize building and maintaining a positive sender reputation through consistent good sending practices, clean lists, and high engagement.
• Monitor deliverability metrics: Regularly monitor your inbox placement and complaint rates. These real-time metrics are far more indicative of your deliverability health than adherence to outdated spam word lists.
• Test subject line effectiveness: Use A/B testing to determine what subject lines resonate best with your audience and drive engagement, rather than relying on generalized avoidance lists. The insights from Word to the Wise often emphasize a data-driven approach to email marketing.

Key findings

• Conciseness: Most documentation recommends keeping subject lines short and to the point, typically under 60 characters or about 9 words, to ensure readability across devices.
• Clarity and honesty: Subject lines should accurately reflect the email's content and not be misleading. Deceptive subject lines are a significant factor in spam complaints and deliverability issues.
• Punctuation and capitalization: Excessive use of exclamation points or all caps is generally advised against, as it can appear spammy or aggressive, even if not a direct filter trigger. For example, Mailchimp suggests limiting punctuation to three marks.
• Personalization: Using personalization, when appropriate, can increase relevance and engagement, improving open rates and overall deliverability.

Key considerations

• CAN-SPAM act compliance: Legal requirements, like the CAN-SPAM Act, explicitly prohibit deceptive subject lines, underscoring the importance of honesty in email marketing. This aligns with advice on email list compliance.
• Relevance over triggers: Focus on crafting subject lines that are relevant and appealing to your specific audience rather than trying to avoid a phantom list of 'spam words' that may not be current.
• Preview text integration: Utilize preview text (preheader text) effectively to complement your subject line and provide additional context, enticing recipients to open the email.
• Avoid false urgency: Documentation often warns against subject lines that create artificial urgency or scarcity, as these can erode trust and lead to negative recipient responses.
• Regular updates: Stay informed about evolving best practices from authoritative sources like Salesforce Marketing Cloud, as filtering algorithms and recipient preferences can change.