Does plain text email version affect deliverability?

Key findings

• Fallback content: Plain text versions serve as a critical fallback, ensuring email content is readable for recipients using text-only email clients, screen readers, or when HTML rendering is disabled or fails.
• Spam filter influence: Some legacy or very strict spam filters may assign a higher spam score to emails that lack a plain text part or where the plain text significantly deviates from the HTML content.
• Auto-generation issues: Automated plain text generation can sometimes produce poor quality content, including excessive use of all capital letters or broken formatting, which might negatively impact deliverability with certain mailbox providers like Microsoft.
• No universal rule: For major ISPs, the absence of a plain text version alone is typically not a primary reason for emails to be blocked or sent to spam, as other factors like sender reputation and content quality hold more weight.

Key considerations

• Content consistency: While an exact match isn't always necessary, ensuring the plain text version conveys the same core message as the HTML can prevent potential filtering issues, though significant mismatches (sometimes referred to as hashbusting) are usually not a major concern for deliverability.
• Manual vs. automated: Manually optimizing the plain text version can improve its quality, but it introduces operational overhead and the risk of human error or content drift. For a deeper dive into technical aspects, read our guide on how including a plain text version improves deliverability.
• Target audience: Consider if a significant portion of your audience relies on plain text emails for accessibility or security reasons. For more on ensuring your emails reach the inbox, refer to this Email on Acid article about plain text emails.
• Overall deliverability: While a plain text version contributes to good email hygiene, fundamental aspects like sender reputation, engagement, and proper authentication (like DMARC, SPF, and DKIM) are far more impactful on your overall inbox placement.

Key opinions

• Low visibility: Many marketers believe that a minimal percentage of their audience (often cited as close to 100%) ever actually sees the plain text version of their emails.
• Quality concerns: Auto-generated plain text is frequently described as "nonsensical crap" due to poor formatting, making it an unappealing fallback for the few who might view it.
• Perceived deliverability impact: Some marketers have anecdotal evidence or hear from contacts in the industry that the absence of a plain text version can lead to emails being blocked by certain email service providers.

Key considerations

• Efficiency vs. perfection: The manual effort required to create a perfect plain text version is often seen as disproportionate to its perceived impact, leading many to rely on automated processes despite their flaws.
• HTML dependency: The focus remains heavily on the HTML version for design and interactive elements, with the plain text version often being an afterthought, but still a required one. Explore the myth of plain text deliverability on Dyspatch.
• Risk of mismatch: There's a concern that manually editing the plain text version could lead to content discrepancies that might confuse recipients or trigger spam filters if not managed carefully. This is similar to how image to text ratio can impact deliverability.

Key opinions

• Minimal impact for major ISPs: For large mailbox providers (like Google, Microsoft, Yahoo), the presence or absence of a plain text version is generally not a significant factor in deliverability decisions.
• ALL CAPS issue: A specific issue arises when auto-generated plain text converts bolded or strong HTML tags into all capital letters. This formatting can be flagged as spam by providers such as Microsoft.
• Old school filters: Some older or highly aggressive spam filters may still penalize emails that lack a plain text part, suggesting it's still a good practice to include one.
• Mismatch tolerance: Occasional mismatches between the HTML and plain text versions are usually not a significant deliverability concern and are unlikely to be treated as hashbusting attempts.

Key considerations

• Scale of protection: Aggressive filtering rules that penalize missing plain text versions are more common in systems protecting a smaller number of mailboxes. Large-scale providers handling millions of emails tend to have more forgiving policies.
• Automated generation for bulk: For high-volume senders, automating the plain text version is a practical necessity, even if it sometimes results in less-than-ideal formatting. Manual creation for every email is often not feasible.
• Testing and adjustment: It is crucial to test how your plain text versions are rendered and whether they contain elements that could trigger spam filters, particularly avoiding the ALL CAPS issue. This attention to detail can help boost email deliverability rates. Also, consider if using bold text affects deliverability.
• Beyond plain text: While useful, the plain text version is a minor factor compared to overall sender reputation, list hygiene, and proper authentication. An expert from Spam Resource often emphasizes focusing on the fundamental principles of good sending to achieve optimal deliverability.

Key findings

• Multipart/MIME standard: The accepted standard for rich emails, RFC 2046 and related specifications, dictates the use of multipart/MIME to encapsulate both HTML and plain text versions within a single email.
• Accessibility mandate: Plain text versions are crucial for web accessibility, enabling users with visual impairments or those using assistive technologies (like screen readers) to access email content.
• Filter heuristic: While not a primary factor, some spam filters consider the presence and quality of the plain text part as one of many heuristics in their scoring algorithms.
• Email client compatibility: Including a plain text version ensures that content is viewable even on older or less sophisticated email clients that may not fully support HTML rendering.

Key considerations

• Content alignment: Documentation often recommends that the plain text version should accurately reflect the content of the HTML version to avoid confusing recipients or triggering spam filters sensitive to content discrepancies.
• Encoding standards: Proper character encoding, such as UTF-8, is critical for the plain text version to render correctly across diverse systems and avoid garbled characters.
• Best practices adherence: Adhering to multipart/MIME standards and providing a well-formatted plain text alternative is considered a fundamental best practice for maximizing deliverability and compatibility, as detailed in various RFCs and industry guides.
• Impact of code quality: The overall quality and size of email code, including its plain text component, influences how easily emails are processed and delivered by receiving servers.