Does using bold text in emails affect deliverability?
Matthew Whittaker
Co-founder & CTO, Suped
Published 28 Apr 2025
Updated 15 Aug 2025
6 min read
One of the most common questions email marketers ask is whether using bold text can negatively affect email deliverability. The concern often stems from a lingering myth that excessive formatting, including bolding, triggers spam filters and lands emails in the junk folder. It's a valid question, as deliverability can be a complex beast with many factors influencing whether your message reaches the inbox or gets caught in a spam trap.
The short answer is, generally, no. Strategic use of bold text in emails is unlikely to harm your deliverability. Modern spam filters are far more sophisticated than they once were. They analyze a multitude of factors, prioritizing sender reputation, email authentication, and overall content patterns over simple formatting choices like bolding. However, like any element of email design, moderation and purpose are key.
HTML versus plain text emails
The idea that bold text affects deliverability is largely a relic from an earlier era of spam filtering. In the past, spammers would often use excessive, flashy formatting, including all caps, bright colors, and heavy bolding, to grab attention. This led early spam filters to flag emails with such characteristics as potentially malicious. As a result, the belief that any unusual formatting, including bold text, could lead to your emails being blacklisted (or blocklisted) became ingrained.
Today, inbox providers like Google and Yahoo employ advanced algorithms that can differentiate legitimate marketing and transactional emails from spam. They consider a much broader context, including sender history, engagement rates, email authentication protocols like DMARC, SPF, and DKIM, and user complaints. A few bolded words in an otherwise well-constructed email are highly unlikely to be the sole reason for deliverability issues.
The real risk isn't the bold tag itself, but rather how it's used. If your email is predominantly bold, or if you're using bolding inconsistently across various text styles, this could potentially appear suspicious to some filters, though it's still less of a concern than other factors. The key is to use it to enhance readability, not to create a chaotic or spammy appearance.
HTML emails
HTML emails allow for rich formatting, including bold text, colors, images, and custom layouts. They are the standard for most marketing and transactional emails today. The concern about formatting often arises with HTML emails due to their complexity.
Deliverability: Modern HTML emails do not inherently have worse deliverability than plain text, provided they are well-coded and follow best practices. Issues arise from poor coding, excessive images, or spammy content.
Usage of bold: Use bold tags (`<b>` or `<strong>`) judiciously for emphasis. Avoid bolding entire paragraphs or large sections.
Plain text emails
Plain text emails contain no formatting, images, or special characters. They are typically used for highly personal communications or for ensuring maximum compatibility across all email clients.
Deliverability: Some argue plain text emails have higher deliverability because they inherently avoid many content-related spam triggers, such as poor HTML, excessive images, or complex styling issues.
Usage of bold: Bold text cannot be directly applied in plain text emails. Emphasis is achieved through other means, such as using asterisks or capitalization (e.g., *important* or IMPORTANT).
Best practices for using bold text
While bold text generally doesn't impact deliverability negatively, it's crucial to use it thoughtfully to maintain a positive sender reputation and ensure your emails are well-received by recipients. The goal is to enhance readability and guide the reader's eye, not to shout or mislead.
Moderate usage: Use bolding sparingly, typically for key phrases, calls to action, or important headings. Avoid bolding entire sentences or paragraphs, which can make your email look cluttered and difficult to read.
Consistency: Maintain a consistent style throughout your email. Inconsistent text styling can be a minor flag for some older filters, although less common now.
Contextual relevance: Only bold text that truly needs emphasis. If everything is bold, nothing stands out.
Accessibility: Ensure your bolded text still has sufficient color contrast with the background for readability, especially for users with visual impairments. This contributes to a positive user experience, which indirectly supports deliverability through engagement.
Remember, the primary purpose of bold text is to make your message clearer and more scannable for the reader. If it serves this purpose without being overdone, it's generally safe to use.
Coding bold text
When using bold text in HTML emails, it's best to use standard HTML tags rather than inline CSS with font-weight. Both `<b>` and `<strong>` tags are widely supported and less likely to cause rendering issues. While `<strong>` is semantically preferred for indicating strong importance, `<b>` is also perfectly acceptable for simple bolding.
Example HTML for bold texthtml
<b>This text is bold.</b>
<strong>This text is also bold.</strong>
Avoid using deprecated tags or overly complex inline styles that could be misinterpreted by different email clients. Clean and simple HTML is always best for deliverability and consistency across platforms.
Beyond formatting: Holistic deliverability
Focusing solely on isolated content elements like bold text can distract from the broader strategies that truly impact whether your emails land in the inbox. A strong sender reputation is paramount, built on consistent engagement, low bounce rates, and minimal spam complaints. If your emails are consistently going to spam, it's rarely just about your formatting.
Other elements like your image to text ratio, the quality of your HTML coding, and even the wording in your subject lines (e.g., using certain 'spammy' words) tend to have a more significant impact. Prioritize building a healthy sending infrastructure and maintaining a clean, engaged email list.
If you're concerned about content elements, the best approach is always to test. A/B testing different email versions, some with more bolding and some with less, can provide valuable insights into how your specific audience and their inbox providers respond. Regularly monitoring your deliverability rates and checking for blocklist appearances will give you the most accurate picture of your email health.
Remember that a positive email experience for your recipients often translates into better deliverability. When users engage with your emails, mark them as not spam, or move them to their primary inbox, it sends strong positive signals to mailbox providers. This proactive approach to improving deliverability is far more effective than worrying about minor formatting details.
Views from the trenches
Best practices
Use bolding to highlight calls to action or key takeaways to improve readability.
Maintain a balanced text-to-image ratio and clean HTML code for overall email health.
Continuously test your email campaigns and monitor deliverability rates to identify any issues.
Segment your audience and personalize content to increase engagement and avoid spam reports.
Common pitfalls
Bolding entire paragraphs or large sections of text, which can appear spammy and reduce readability.
Using inconsistent or overly complex styling that can confuse email clients and spam filters.
Ignoring overall email health metrics while focusing too much on minor formatting details.
Failing to adapt email design based on A/B testing results and audience engagement data.
Expert tips
Implement email authentication protocols like DMARC, SPF, and DKIM to bolster sender reputation.
Regularly clean your email lists to remove inactive or invalid addresses, reducing bounce rates and spam trap hits.
Personalize content and sending times to improve recipient engagement and signal positive intent to mailbox providers.
Prioritize mobile responsiveness in your email design, as most users now access emails on mobile devices.
Marketer view
Marketer from Email Geeks says they have never heard about bolded text causing deliverability issues.
2020-09-29 - Email Geeks
Marketer view
Marketer from Email Geeks says that filters were previously concerned about the distribution of different styles because spammers often sent HTML emails.
2020-09-29 - Email Geeks
Final thoughts on bold text and deliverability
In summary, the notion that using bold text in emails directly harms deliverability is largely outdated. While excessive or chaotic formatting was once a red flag for spam filters, modern systems are far more advanced, focusing on overall sender reputation, authentication, and user engagement.
You can use bold text to improve readability and highlight important information without fear of being blocklisted, provided you use it moderately and purposefully. Prioritize holistic email deliverability strategies, such as maintaining a clean list, authenticating your emails, and crafting engaging content, to ensure your messages consistently reach the inbox.
