Ensure flawless email delivery by automatically removing hidden non-printable characters that trigger spam filters or disrupt formatting.
Campaign Cleaner scans your email HTML for invisible control characters and non-printable codes, then removes them automatically - so your email formats correctly and doesn't get flagged before it even reaches the inbox.
Quick Overview of Features
Control characters are non-printable characters defined in the ASCII and Unicode standards. They were originally designed to control output hardware like printers and terminals - characters like "form feed" to advance to a new page, or "null" to signal the end of a string. They are invisible to the human eye but exist as real bytes in the underlying text.
In email HTML, these characters have no legitimate purpose. They do not render anything visible, they do not control any email client behavior, and they are not part of any valid HTML syntax. Their only effect is to add unexpected bytes to your email's code - bytes that spam filters and mail transfer agents can detect and react to.
The most common source is copy-pasting content from desktop applications. Word processors like Microsoft Word, PDF readers, and spreadsheet tools embed invisible formatting codes in their text. When that content is pasted into an email editor or HTML template, those codes travel along invisibly and end up in the final HTML.
Other sources include CRM and marketing platform exports that don't sanitize database content before inserting it into email templates, automated HTML generators that don't validate their output encoding, and legacy systems that produce content in encodings other than UTF-8 where certain byte values map to control ranges.
Spam filters examine the raw byte content of email, not just the rendered output. Non-printable characters in unexpected positions are a known indicator of obfuscation - a technique used in malicious email to hide content from automated scanners while still displaying it to human readers. Filters assign penalty points when they encounter these patterns.
SpamAssassin has specific rules that fire on various types of unusual byte sequences in email bodies. Even if your email content is entirely legitimate, the presence of stray control characters can push your spam score above the threshold and land your message in the junk folder. Removing them is a straightforward fix that costs nothing in terms of visible content.
Different email clients handle unexpected bytes differently. Some silently discard them, some render them as visible replacement characters (the small box or question mark symbol), and some let them interfere with HTML tag parsing. A control character embedded inside an HTML attribute value can cause the attribute to be treated as malformed, breaking the styling or link that attribute was meant to provide.
In Outlook in particular, which uses Word's HTML rendering engine, unexpected bytes in certain positions can cause layout shifts, extra spacing, or content truncation. The variability across clients makes control characters especially risky - your email might look fine in your sending platform's preview but fail in ways that are hard to diagnose once it reaches recipients.
Campaign Cleaner scans your email HTML at the byte level. It identifies any character that falls outside the permitted set - keeping standard whitespace characters (tab, newline, carriage return) that are valid in HTML, while stripping all other non-printable codes. The scan covers the entire email including tag content, attribute values, and text nodes.
The removal is non-destructive to visible content. Because control characters are invisible and have no display function, removing them produces HTML that looks and renders identically to the original - just without the invisible problematic bytes. The result passes cleanly through spam filters and renders consistently across all major email clients.
Are You Ready To Experience The Difference?
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.
