Campaign Cleaner scans your email HTML for comment blocks, removes them automatically, and preserves any Outlook conditional comments your layout requires - so your email is leaner, cleaner, and less likely to be flagged before it reaches the inbox.
Quick Overview of Features
HTML comments are markup constructs that begin with <!-- and end with -->. Everything between those delimiters is treated as a comment and ignored during rendering. They originated as a developer tool for annotating code, temporarily disabling markup, or leaving notes for team members. In email HTML they often arrive as inherited artifacts: notes from the original template designer, markers left by a CMS or email builder, or blocks of old code commented out during revisions.
They are invisible to recipients in normal rendering but exist in full in the raw HTML that spam filters, mail transfer agents, and source-viewing recipients can all read.
Spam filters do not render your email - they read it. Filters process every byte of your HTML including everything inside comment tags. If a comment contains a word or phrase that appears in a spam rule - and internal development notes frequently contain language like "free", "offer", "price", or "urgent" - that content contributes to your spam score even though no recipient will ever see it.
Additionally, large volumes of comment markup can look suspicious to filters that evaluate the ratio of visible-to-invisible content in an email. Removing all comments before sending gives filters nothing extra to evaluate and keeps your content ratio clean.
Every character in your HTML costs bytes. Email clients like Gmail clip messages that exceed a certain HTML file size - currently around 102KB - which means recipients see a "Message clipped" notice and must click to view the full email. Comment accumulation in long-lived templates can be substantial: it is not unusual for a mature email template to carry several kilobytes of comment markup from previous development cycles.
Smaller HTML also parses and renders faster. Lean, comment-free HTML is a mark of a well-maintained template and one less variable to troubleshoot when investigating rendering inconsistencies across clients.
Recipients who are technically curious can view the raw HTML source of any message through their email client's developer tools or "view source" option. Any comments in your code are fully readable. Internal team notes, content strategy annotations, A/B test markers, pricing strategy discussions, or client-specific customization notes can all be exposed this way.
Removing all standard HTML comments from outbound email is a simple hygiene step that eliminates a category of potential embarrassment or information leakage entirely.
Not everything that looks like a comment in email HTML should be removed. Microsoft Outlook uses conditional comments to deliver Outlook-specific HTML. These take the form of <!--[if mso]> ... <![endif]--> and are processed by Outlook's rendering engine despite looking like HTML comments to every other client. They are how email developers provide Outlook-compatible table layouts and other Outlook-specific elements.
Campaign Cleaner distinguishes between standard HTML comments and Outlook conditional comments. Standard comments are removed. Conditional comments are preserved exactly as they are. You do not need to manually protect your Outlook-specific code before running a cleanup.
Become a part of the Campaign Cleaner community today, and join countless satisfied customers who have witnessed significant improvements in their email deliverability and campaign success. Don’t let HTML issues hold you back; let Campaign Cleaner optimize your campaigns and boost your inbox rates.
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