How does HTML coding affect email deliverability and are emojis safe to use in email marketing?
Matthew Whittaker
Co-founder & CTO, Suped
Published 27 Jun 2025
Updated 15 Aug 2025
7 min read
When sending emails, the underlying HTML code and content elements like emojis play a significant role in determining whether your messages land in the inbox or the spam folder. It's not just about what you say, but also how it's structured and presented to mailbox providers.
Email deliverability is a complex dance between sender reputation, authentication, and content quality. While sender reputation often takes precedence, the actual HTML coding and design choices can trigger spam filters or negatively influence recipient engagement, leading to deliverability issues over time.
Emojis have become ubiquitous in digital communication, including email marketing. They can grab attention and convey emotion, but their safety and impact on email deliverability are often debated. We'll explore how both your HTML coding practices and the strategic use of emojis affect whether your emails reach their intended audience.
How HTML affects email deliverability
Clean, valid HTML is a cornerstone of good email deliverability. Mailbox providers and spam filters analyze your email's code for anything that looks suspicious or indicates poor coding practices, which can be a red flag. Overly complex, broken, or malformed HTML can signal that your email is not legitimate. For example, some anti-spam systems can "fingerprint" pieces of code that have a history of being associated with abusive content.
Specific HTML patterns can significantly impact your inbox placement. This includes things like hidden text, which spammers often use to evade filters, or URLs that mask other URLs, resembling phishing attempts. Using URL shorteners indiscriminately can also raise suspicion. Additionally, if you frequently reuse content or templates that have been previously identified in spam campaigns, services like Cloudmark might fingerprint your content, leading to blocked or junked emails. For more on this, understand how malformed HTML impacts deliverability.
Ensuring your HTML looks like that of legitimate emails and avoiding patterns found in malware, spam, or phishing attempts is paramount. This includes proper formatting of links. Mailbox providers, such as Google, outline sender guidelines that touch on content quality. Adhering to these general best practices for your email code quality and size can significantly improve your deliverability, helping your emails bypass spam filters and reach the inbox.
Problematic HTML elements to avoid
URLs not FQDN: Links using IP addresses instead of fully qualified domain names, e.g., https://123.123.123.124, are often seen as suspicious by spam filters.
Masked URLs: When the displayed link text differs significantly from the actual URL, it can mimic phishing attempts, e.g., <a href="one URL">A different URL</a>.
Hidden text: Using invisible text (e.g., matching text color to background) to stuff keywords or evade detection is a common spam tactic.
URL shorteners: While convenient, excessive use of URL shorteners, especially from less reputable services, can trigger spam filters.
Reused content: Templates or code snippets frequently used in spam campaigns can be fingerprinted by spam services, leading to deliverability issues.
Emojis in email marketing: Balancing engagement and deliverability
Emojis can significantly enhance your email marketing campaigns by making subject lines more engaging and email content more visually appealing. Studies show that a well-placed emoji can increase open rates by attracting attention in a crowded inbox. They can convey tone and emotion efficiently, sometimes replacing several words and adding a touch of personality to your brand messaging.
However, using emojis without caution can pose deliverability risks. Overuse or inappropriate emojis can sometimes trigger spam filters, especially if they are commonly associated with spammy content. More importantly, if a significant percentage of your recipients find your emoji usage unprofessional or spammy and mark your emails as junk, this negative feedback directly impacts your sender reputation and, consequently, your deliverability. This applies to all aspects of your email that recipients can see or read.
The placement of emojis matters. While emojis in subject lines are popular for standing out, they carry a slightly higher risk than emojis in the email body. It's crucial to understand your audience and their preferences. What works for a B2C fashion brand might not be appropriate for a B2B tech company. Always test how your audience responds to emojis in different contexts to determine their effectiveness for your specific campaigns. Learn more about whether all-emoji subject lines hurt deliverability.
Pros of using emojis
Higher open rates: Emojis can make your emails stand out in a crowded inbox and increase their visibility, leading to more opens. This is a common finding, as detailed in an article on email emojis.
Improved engagement: They can create a more personal and relatable tone, boosting engagement with your content.
Brand personality: Emojis can reinforce your brand's voice and make your communications more memorable.
Space-saving: Especially in subject lines, emojis convey meaning efficiently, saving valuable character space.
Cons of using emojis
Spam trigger risk: Some emojis, or excessive use, might be associated with spam and could trigger filters.
Negative user feedback: If recipients find emojis unprofessional or annoying, they might mark your emails as spam, damaging your reputation.
Rendering inconsistencies: Emojis can appear differently across various email clients, devices, and operating systems, potentially leading to broken characters or unintended displays.
Professionalism perception: In certain B2B or formal contexts, emojis might be perceived as unprofessional, detracting from your message.
Technical considerations for optimal deliverability
Proper character encoding is critical for displaying your email content correctly, especially when using special characters or emojis. UTF-8 is the recommended encoding for emails as it supports a wide range of characters, including all emojis. Without the correct Content-Type header, emojis can render as broken characters or question marks, diminishing the user experience and potentially flagging your email. Check our guide on UTF-8 vs Base64 encoding.
The overall size of your email's HTML also matters. Overly large HTML can lead to inbox clipping, especially in email clients like Gmail, where emails exceeding a certain size (typically 102KB) get truncated. This can hide important calls to action or unsubscribe links, frustrating recipients and leading to negative engagement. Maintain a lean HTML structure to ensure your entire message is visible upon opening. Our article on HTML email size and its impact can provide further insights.
Ensuring proper URL formatting within your HTML is also a technical consideration. Mailbox providers scrutinize links to detect phishing and malicious content. This means avoiding unencoded or non-fully qualified domain name (FQDN) URLs, as well as disguised links. All links should be clear, functional, and point to reputable domains. Unencoded URLs, for example, can appear suspicious. Here's a standard Content-Type header:
Recommended content type header
Content-Type: text/html; charset="UTF-8"
The balance of code and creativity for email deliverability
HTML coding significantly influences email deliverability. While it might seem less impactful than sender reputation, clean, valid code that avoids suspicious patterns is essential. Malformed HTML, hidden text, or obfuscated links can trigger spam filters and damage your sending reputation. Regularly review your email templates and ensure they adhere to email coding best practices, focusing on simplicity and clarity.
Regarding emojis, they are generally safe to use in email marketing when applied thoughtfully. They can boost engagement and open rates by adding visual appeal. However, context, audience, and moderation are key. Overuse, especially in subject lines, or using emojis that don't resonate with your audience, could lead to negative feedback (like spam complaints), which would, in turn, hurt your deliverability. Always A/B test your emoji usage to see what performs best for your subscribers.
Ultimately, achieving high email deliverability is a holistic effort. It combines strong sender authentication (like DMARC, SPF, and DKIM), a healthy sending reputation, good list hygiene, and optimized email content, including clean HTML and strategic emoji usage. By paying attention to these details, you can significantly increase the chances of your emails reaching the inbox.
Views from the trenches
Best practices
Always use fully qualified domain names (FQDNs) for all URLs in your email HTML, rather than IP addresses or masked links, to build trust.
Ensure your email HTML is clean and simple, avoiding excessive nesting, inline styles, or deprecated tags that can flag spam filters.
Utilize UTF-8 encoding consistently across all email content, especially when incorporating special characters or emojis, to prevent rendering issues.
Keep your HTML email size optimized to prevent clipping in major email clients like Gmail and ensure the full message is visible.
A/B test emoji usage in both subject lines and email bodies to understand your specific audience's reception and optimize for engagement without compromising deliverability.
Common pitfalls
Using hidden text, suspicious URL masking, or other HTML techniques commonly associated with spam can severely damage your sender reputation.
Relying on generic or frequently reused email templates might trigger content-based spam filters if those templates have a history of being used for abusive content.
Ignoring the Content-Type header or using incorrect character encoding can lead to broken characters and emojis, making your emails appear unprofessional and untrustworthy.
Failing to monitor how recipients react to your email content, including emoji use, can result in high spam complaint rates that negatively impact deliverability.
Including unencoded URLs or using too many URL shorteners can make your emails appear suspicious to mailbox providers and lead to blocked messages.
Expert tips
Content reputation is as crucial as IP/domain reputation, especially for inbox vs. spam folder decisions.
Arbitrary fingerprinting and rule-based filters by anti-spam systems can identify problematic HTML patterns.
The hostnames of URLs in your HTML body often dominate content reputation decisions by mailbox providers.
While rare, some individual mail server administrators might set up rules against emojis; however, it's generally an infinitesimally small factor.
Continuously observe recipient engagement metrics to gauge the true impact of your HTML and emoji choices on deliverability.
Expert view
Expert from Email Geeks says content plays a less important role than IP/domain reputation, but certain HTML aspects like non-FQDN URLs, masked URLs, hidden text, URL shorteners, and reused content can cause significant deliverability issues.
2021-02-24 - Email Geeks
Expert view
Expert from Email Geeks says HTML coding can affect deliverability, even if limited. Beyond special characters and broken tags, anti-spam systems can "fingerprint" code snippets previously associated with abusive content.
Gmail, where emails exceeding a certain size (typically 102KB) get truncated. This can hide important calls to action or unsubscribe links, frustrating recipients and leading to negative engagement. Maintain a lean HTML structure to ensure your entire message is visible upon opening. Our article on HTML email size and its impact can provide further insights.
