Are spam trigger words, PDF attachments, and links bad for email warm-up and deliverability?

Key findings

• Outdated concern: The impact of specific spam trigger words on email deliverability is largely an outdated concern. Modern spam filters (or blocklists) are far more sophisticated, analyzing overall sender reputation and engagement rather than isolated keywords. Learn more about whether email spam trigger words are still relevant.
• PDF attachments are detrimental: Directly attaching PDFs to emails, especially from new domains, is highly risky. PDFs are a common vector for malware, increasing the likelihood of emails being flagged as spam or silently discarded by corporate mail filters. This can significantly negatively impact deliverability.
• Links are generally safe: Including links to your website or legitimate content is generally neutral to positive for deliverability, provided your domain has a good sending reputation. It is a much safer alternative to attachments for sharing documents or catalogs. However, be cautious with third-party URL shorteners, which can sometimes be blocklisted.
• Warm-up considerations: During the warm-up phase, focusing on building a positive sender reputation through consistent, engaged sending is paramount. Avoid anything that might appear suspicious, such as attachments or overly promotional content, regardless of whether a specific spam trigger word is present.

Key considerations

• Reputation is key: Focus on building and maintaining a strong sender reputation. This is far more impactful than obsessing over individual words or minor content elements. Learn about how to improve your domain warm-up.
• Avoid attachments: Unless absolutely necessary and for a highly engaged audience, avoid direct PDF attachments. They pose a significant deliverability risk. Mailjet's blog emphasizes rethinking PDFs in your emails.
• Prefer direct links: Link directly to content hosted on your website or reputable cloud services instead of attaching files. This provides a safer and more reliable delivery path.
• Monitor performance: Regularly monitor your email campaign performance during warm-up and beyond. Pay attention to inbox placement rates and recipient engagement metrics to identify and address any issues promptly.

Key opinions

• Keyword fears are fading: Many marketers acknowledge that strict keyword filtering is largely a thing of the past. They've observed that once-problematic words, even in subject lines, no longer automatically trigger spam filters.
• Attachments are high risk: There's a strong consensus that email attachments, particularly PDFs, are risky and can significantly harm deliverability, especially for new or less established senders. They are seen as potential spam triggers and malware vectors.
• Linking is preferred: Marketers generally prefer linking to content on their website or cloud storage over direct attachments, recognizing it as a safer approach to share information without impacting sender reputation.
• Domain reputation concerns: Some marketers consider extreme measures like avoiding links altogether or using attachments to bypass perceived domain reputation issues, indicating a lack of clarity on how to properly warm up a new IP or domain.

Key considerations

• Prioritize recipient engagement: Focus on delivering relevant content that recipients want to engage with. Positive engagement signals are crucial for deliverability, far outweighing concerns about specific words. Refer to our guide on best practices for avoiding spam filters.
• Avoid unnecessary attachments: Even if you're not a new sender, attachments should be used sparingly. Campaign Refinery points out that attachments can trigger spam traps.
• Use trustworthy links: Ensure all links in your emails lead to reputable domains and are directly relevant to your content. Avoid suspicious or blocklisted URL shorteners. You can find out more on if linking to PDFs is bad for deliverability.

Key opinions

• Spam words are mostly a myth: Experts widely contend that the concept of specific spam trigger words is largely outdated. Modern filters assess overall context and sender behavior.
• Rare, unpredictable keyword issues: While rare, major mail providers might occasionally introduce unexpected keyword filtering for specific, non-obvious terms, but these instances are infrequent and unannounced.
• Attachments are a serious red flag: PDF attachments are consistently highlighted as a major risk. They are associated with malware and are heavily scrutinized by corporate mail filters, often leading to silent discard or direct spam folder placement.
• Linking is safe if reputable: Links to your website are generally considered neutral to positive for deliverability if your domain has a good reputation. They are seen as a legitimate way to drive traffic and engagement.
• Context is king: The overall context of your email, including sender reputation, recipient engagement, and content relevance, matters far more than individual words or formatting choices.

Key considerations

• Focus on reputation first: During warm-up, focus on sending clean, highly engaging content to opted-in users to build a positive sender reputation. This foundation will mitigate most content-related concerns.
• Avoid direct attachments: Never attach files for marketing or mass emails. This practice can severely impact deliverability and lead to immediate blacklisting or silent discarding. Find out more about how PDFs impact deliverability.
• Link to hosted content: Always link to documents, catalogs, or other resources hosted on your own website or a trusted cloud service. Even cloud-hosted PDF links can sometimes raise flags if not formatted correctly. Our article on direct PDF download links provides further insights.
• Understand filter evolution: Keep up to date with modern spam filtering techniques. SpamResource highlights the irrelevance of spam trigger words for deliverability.

Key findings

• Attachments are a spam trigger: Documentation frequently warns that email attachments can trigger spam traps and significantly damage deliverability, often being restricted by email marketing tools.
• Impact on sender reputation: Emails with PDF attachments, if flagged by spam filters, can directly harm the sender's reputation, as email service providers monitor such occurrences.
• Third-party links are risky: Third-party URL shorteners are often advised against, as they are commonly found on email blocklists, which negatively impacts deliverability.
• Content optimization is vital: Comprehensive guides emphasize optimizing content and building domain authority as primary methods for avoiding spam filters and improving overall deliverability. This includes understanding the impact of your email size on spam traps.

Key considerations

• Prioritize direct links over attachments: To maintain a healthy sender reputation, technical documentation consistently recommends linking to content hosted securely on your website rather than attaching files, especially for bulk or marketing emails. This is critical for avoiding negative impacts from PDF links.
• Maintain domain authority: Building and preserving a strong domain authority is emphasized as a foundational element for bypassing spam filters, as it signals trustworthiness to mail providers. Learn about how to improve domain reputation.
• Implement authentication protocols: Documentation often advises implementing email authentication protocols like SPF, DKIM, and DMARC to prevent spoofing and enhance deliverability. Zoho's guide highlights placing protocols in place to avoid spoofing.