When talking about email deliverability, the focus often goes to sender reputation, IP addresses, or authentication protocols. However, a question that frequently comes up is whether the actual HTML template used for an email can impact its ability to reach the inbox. It's a valid concern, especially when switching email service providers (ESPs) or updating email builders, as seemingly minor changes can lead to unexpected deliverability shifts.
There are cases where a new template appears to cause delivery issues, like an increase in bounces. For instance, if you're warming up a new IP address with a new mailing system and switch from an old HTML template to a new one, you might notice a sudden rise in bounces, especially from specific mailbox providers. This suggests that the template itself could be a factor in how your emails are perceived by spam filters and recipient inboxes.
While HTML templates don't directly determine deliverability in the same way your sender reputation does, certain aspects of their construction and content can definitely influence how mailbox providers evaluate your messages. Understanding these nuances is key to ensuring your beautifully designed emails actually land where they're intended.
The hidden impact of HTML size
One of the most immediate ways an HTML template can affect deliverability is through its file size. Mailbox providers, such as Gmail and Outlook, are wary of overly large emails, which can be a red flag for spam. Industry best practices suggest keeping your HTML email file size under 100KB. Anything larger can increase the likelihood of your email being flagged or truncated, negatively impacting the user experience and potentially your inbox placement.
Excessive HTML code, especially that which is not optimized, contributes to larger file sizes. This includes complex styling, redundant tags, and bloated code from drag-and-drop builders. While a well-crafted HTML email will get delivered, overly complex or unoptimized HTML can slow down loading times and signal suspicious content to spam filters.
Many email marketing platforms offer tools to check email file sizes, but it's important to understand that exceeding this limit can directly impact email deliverability. Pay close attention to how your template’s size compares to this benchmark.
HTML size best practices
Keep it under 100KB: This is a generally accepted benchmark to avoid deliverability issues due to size.
Optimize images: Large images significantly contribute to file size. Compress them and host externally.
Minify code: Remove unnecessary spaces, comments, and redundant CSS from your HTML.
Avoid unnecessary elements: Streamline your template's structure to reduce overall code volume.
Code quality and rendering issues
Beyond just size, the quality of your HTML code and how it's structured can significantly influence deliverability. Malformed HTML, broken tags, or unsupported CSS can cause rendering issues across different email clients, which in turn can trigger spam filters. Mailbox providers prioritize a consistent and secure user experience, so emails that look suspicious or break in certain clients are more likely to be diverted to the spam folder.
Common culprits include excessive spacing, numerous blank table rows, or hidden text elements. These are often indicators of spamming tactics and can result in your emails being flagged. It's crucial to check your templates for these issues and ensure they are clean and valid. Even simple errors can cause problems with filters.
Validate HTML: Use an HTML validator to catch and fix any errors or malformed tags.
Inline CSS: Many email clients have limited support for external or embedded stylesheets.
Responsive design: Ensure your template renders correctly on all devices and screen sizes.
Common HTML pitfalls
Excessive spacing: Too many blank lines or empty table cells can be perceived as suspicious.
Hidden text: Using white text on a white background to stuff keywords is a classic spam tactic.
Unsupported elements: Elements like JavaScript can trigger spam filters and won't render in email clients.
Content elements and design choices
The content elements within your HTML template also play a critical role. While HTML emails offer rich formatting and visuals, certain design choices can hurt deliverability. For example, image-only emails are generally bad for deliverability. They often lack sufficient text-to-image ratio, which can be seen as suspicious by filters. Moreover, if images don't load, recipients see an empty email, leading to a poor experience and potentially marking your email as spam.
Another factor is the presence and reputation of your link tracking domains and image hosting domains. If these domains are newly created or have a poor reputation (e.g., they're on a blacklist), it can severely impact your email's deliverability. This is especially relevant if you've recently migrated ESPs, as the new provider might use different tracking domains than your previous one. Consider also if you're using HTTP instead of HTTPS links, which can raise security concerns for mailbox providers.
While plain text emails might seem to offer better deliverability for cold outreach due to their simplicity and personal feel, HTML emails, when done correctly, have a high chance of delivery and offer more engagement. The key is to balance visual appeal with deliverability best practices. Ensuring your images have alt text and a balanced text-to-image ratio is also crucial, as is understanding how images in emails affect deliverability.
Content element
Impact on deliverability
Mitigation
Image-only emails
High spam risk, poor user experience if images don't load.
Ensure good text-to-image ratio, always use alt text.
Javascript/scripts
Not supported by most email clients, flags spam filters.
Do not include any executable scripts in your HTML.
Can cause rendering issues and potential deliverability flags.
Use web-safe fonts or embed fonts carefully with fallbacks.
Beyond the template: sender reputation
While the HTML template itself isn't the sole arbiter of deliverability, issues within the template can negatively affect your sender reputation. A poor sender reputation is a primary reason emails end up in spam folders or get bounced. Mailbox providers build trust based on your sending habits, recipient engagement, and compliance with best practices. A template that consistently triggers spam filters, leads to low engagement, or results in recipient complaints will damage this trust.
For instance, if a new template causes a significant increase in bounces, as seen with some BTInternet recipients, this signals to the receiving server that your content might be problematic. Such signals can lead to your sending IP or domain being added to a blocklist (or blacklist), which then affects all emails sent from that source, regardless of the template used. This is why it's so important to understand how email blacklists actually work.
It's a cascading effect: a problematic template can lead to poor engagement, increased complaints, bounces, and ultimately, a damaged sender reputation. This, in turn, makes it harder for any of your emails to reach the inbox. Therefore, while templates don't directly determine deliverability, they are a significant component of your overall email program that contributes to your sender reputation. This is also how an email template can trigger spam filters and cause issues.
Example SPF recordDNS
v=spf1 include:_spf.example.com ~all
Views from the trenches
Best practices
Always include a plain text version of your HTML email. This provides a fallback for clients that don't render HTML and can improve deliverability.
Test your HTML templates across various email clients and devices to catch rendering issues before sending.
Keep your HTML clean and simple. Avoid excessive nesting of tables and unnecessary code.
Common pitfalls
Sending image-only emails without sufficient text or alt attributes, which can trigger spam filters.
Including JavaScript or other unsupported dynamic content within email HTML, leading to rendering issues.
Using hidden text or excessive white space to manipulate email size or content, raising spam flags.
Expert tips
Ensure your email template is responsive across all devices and email clients.
Validate your HTML and CSS to ensure it's well-formed and adheres to email client standards.
Monitor your engagement metrics closely after template changes to detect deliverability shifts.
Marketer view
Marketer from Email Geeks says they experienced differences in deliverability with different HTML templates, noting that an old template worked fine while a new one led to 100% bounces from BTInternet, which suggests a template-related issue even with a new IP warming.
2019-05-22 - Email Geeks
Expert view
Expert from Email Geeks says that when switching ESPs, deliverability issues could be related to the new IP addresses or the reputation of a new subdomain, advising to check for the exact bounce error message.
2019-05-22 - Email Geeks
Key takeaways for template and deliverability success
While email HTML templates don't directly control deliverability, their construction and content choices significantly influence how mailbox providers perceive your emails. Factors like HTML file size, code quality, and the nature of included content (like images and links) can all contribute to whether your messages land in the inbox or the spam folder.
Ultimately, a well-coded, optimized, and user-friendly HTML template supports good deliverability by enhancing recipient engagement and avoiding spam triggers. Regularly reviewing and optimizing your templates as part of your overall email strategy is essential to maintaining a strong sender reputation and ensuring your messages reach their intended audience. Addressing why your emails are going to spam involves a holistic approach, and your HTML template is a crucial piece of that puzzle.
Gmail and 
Outlook, are wary of overly large emails, which can be a red flag for spam. Industry best practices suggest keeping your HTML email file size under 100KB. Anything larger can increase the likelihood of your email being flagged or truncated, negatively impacting the user experience and potentially your inbox placement.
BTInternet recipients, this signals to the receiving server that your content might be problematic. Such signals can lead to your sending IP or domain being added to a blocklist (or blacklist), which then affects all emails sent from that source, regardless of the template used. This is why it's so important to understand how email blacklists actually work.
