Content check in the Email Designer content-check
Journey Optimizer includes automated technical validation directly in the Email Designer, helping you catch HTML and CSS issues before sending.
Results are surfaced as errors, warnings, or informational notices in the authoring panel, with contextual details and one-click fixes where available, so issues can be resolved without leaving the Email Designer.
Access content checks access-content-checks
Content checks are always available in the Email Designer. To view them, click the Issues icon in the right rail to open the Content check pane — all detected issues are listed there.
Checks are surfaced with three severity levels:
When no issues are detected, the pane displays No issues detected and the corresponding icon is green.
Depending on the issue, you can view more context, apply a one-click fix, or save your email to refresh a check result.
- For some detected issue, you can click the Show details button to see more context. Click Hide details to collapse.
- Similary, you can click the Show fix button and apply a one-click fix where available. If the fix cannot be applied automatically, a messsage is displayed and you must manually solve the issue.
Recalculation of checks recalculation
Most checks — such as unsupported HTML elements, empty divs, and HTML size — are recalculated each time you edit your email, so they always reflect your current content.
Other checks, such as CSS size, are calculated from the serialized content — the version of your email as it is loaded or saved — not from the live editing state in the Email Designer. In this case, the saved content can differ slightly from what you see while editing. If you make edits without saving, a Stale check label appears to indicate the result may no longer be accurate. Save your email to refresh the calculation.
Fix detected issues fix-issues
The tables below list all possible messages and the recommended action for each. Expand the category matching the message you see in the Content check pane.
| table 0-row-3 1-row-3 2-row-3 3-row-3 4-row-3 | ||
|---|---|---|
| Message | Severity | What to do |
Your content contains a <script> tag, which is not supported in any email system. Remove it to avoid delivery and rendering issues. |
Error | Locate and remove all <script> tags from your HTML content. |
Your content contains a <base> tag, which can cause link and resource resolution issues in the Email Designer. To fix, you need to remove it. |
Error | Remove the <base> tag from your HTML. |
| Your content contains an HTML meta tag with refresh, which is not supported in the Email Designer. Remove it to prevent unexpected behavior. | Warning | Remove the meta refresh tag from your HTML. |
| Your content contains empty divs, which can cause layout issues in Microsoft Outlook (MSO). To fix this, remove the empty divs and use the spacing of sibling elements instead. | Warning | Delete the empty <div> elements and adjust padding or margin on surrounding elements to maintain spacing. |
| table 0-row-3 1-row-3 2-row-3 3-row-3 4-row-3 | ||
|---|---|---|
| Message | Severity | What to do |
| Total CSS size exceeds Gmail’s 16 KB limit and will cause rendering issues in Gmail. | Error | Use Apply fix to remove unused CSS rules automatically, or manually simplify your styles. |
| Total CSS size is close to Gmail’s 16 KB limit and could cause rendering issues if more CSS is added. | Warning | Use Apply fix to remove unused CSS rules, or reduce styles before adding more content. |
| Total CSS size for this fragment exceeds 3 KB. Combining this with other fragments could cause the total email CSS to exceed Gmail’s 16 KB limit and cause rendering issues. | Warning | Simplify the CSS in this fragment to keep the combined email CSS under 16 KB. |
| Content contains unused CSS rules. This could cause rendering issues in Gmail. | Warning | Use Apply fix to automatically remove CSS rules that reference elements no longer present in the email. |
| table 0-row-3 1-row-3 2-row-3 3-row-3 | ||
|---|---|---|
| Message | Severity | What to do |
| Estimated HTML size exceeds Gmail’s 100 KB limit and will cause rendering issues in Gmail. The actual HTML size may differ at send time. | Error | Reduce email content — remove unnecessary elements, simplify structure, or split content across multiple sends. |
| Estimated HTML size is close to Gmail’s 100 KB limit and could cause rendering issues if more HTML is added. The actual HTML size may differ at send time. | Warning | Simplify content before adding more. Emails exceeding the Gmail limit will be clipped for recipients. |
| Estimated HTML size for this fragment exceeds 20 KB. Combining this with other fragments could cause the total email HTML to exceed Gmail’s 100 KB limit and cause rendering issues. The actual HTML size may differ at send time. | Warning | Reduce the HTML in this fragment to keep the combined email size under Gmail’s 100 KB limit. |
About HTML and CSS size size-estimation
HTML and CSS size values shown in the Email Designer are estimates computed at authoring time. They reflect the full rendered payload as it exists in the editor at that moment, and include:
- HTML structure – all markup, tags, layout wrappers, and inline styles
- Inlined CSS – Email Designer inlines styles before calculating size, which is standard for email clients but inflates the raw figure compared to an external stylesheet
- Text content – all copy and personalization tokens, counted at their placeholder length (not their resolved value)
- Fragments – all referenced fragments are expanded inline, so each fragment contributes its full HTML/CSS weight to the total
- Conditional blocks (if-else) – all branches are included in the size estimate at authoring time, because conditions are not evaluated until send time
- Images – only the image reference (src URL) is counted, not the binary image data itself
Why the estimate can differ from the delivered size size-estimate-difference
The size shown is a worst-case upper-bound estimate, not the exact email a recipient will receive. It may differ for the following reasons:
- Conditional content: At send time, only the branch matching the recipient’s profile is rendered. A template showing 120 KB in the editor might produce a 60 KB email for most recipients.
- Personalization tokens: Placeholder tokens are counted at their raw token length. Resolved values are usually shorter.
- HTML size optimization: If the Optimize HTML size option is enabled, whitespace, comments, and redundant characters are stripped at send time, reducing the final payload. Learn more
What size warnings mean for authors size-warnings
Size warnings (for example, HTML exceeding 100 KB) are proactive signals to help you optimize your email before sending — they are not hard blocks, and they do not reflect the exact size recipients will see. They exist to help avoid:
- Emails being clipped by Gmail, which clips messages at approximately 102 KB of HTML
- Slow rendering on mobile devices or on low-bandwidth connections
This section contains structured knowledge intended to support interpretation, retrieval, and question answering related to this topic.
For complete understanding, this information should be combined with the documentation on this page. Neither source is intended to stand alone; the page describes the feature, while this section provides additional context that helps disambiguate terminology, intent, applicability, and constraints.
- TL;DR: Content checks in the Email Designer automatically detect HTML and CSS issues before sending, surfacing them as errors, warnings, or informational notices with contextual details and one-click fixes where available.
Intents:
- Catch HTML and CSS issues in an email before sending
- Open the Content check pane from the Issues icon in the right rail to review all detected issues
- Apply a one-click fix or view details for a detected issue
- Understand the Error, Warning, and Info severity levels
- Understand why estimated HTML and CSS sizes can differ from the delivered email
- Refresh a stale check by saving the email
Glossary:
- Content check: Automated technical validation in the Email Designer that detects HTML and CSS issues before sending (product-specific)
- Stale check: A label indicating that a check result (such as CSS size, calculated from serialized content) may no longer be accurate because edits were made without saving (product-specific)
- Serialized content: The version of the email as it is loaded or saved, used to calculate certain checks such as CSS size, rather than the live editing state (product-specific)
- Optimize HTML size: An option that strips whitespace, comments, and redundant characters at send time to reduce the final payload (product-specific)
Guardrails:
- Three severity levels: Error (Red — critical issue causing delivery or rendering failures; resolve before sending), Warning (Orange — potential issue that may affect rendering in specific email clients; recommended to review and resolve), Info (Blue — does not block sending but may affect long-term maintainability).
- Total CSS size exceeds Gmail’s 16 KB limit causes rendering issues in Gmail (Gmail-imposed limit); a fragment whose CSS exceeds 3 KB is flagged because combining fragments could push the total email CSS over the 16 KB limit.
- Estimated HTML size exceeds Gmail’s 100 KB limit causes rendering issues in Gmail (Gmail-imposed limit); Gmail clips messages at approximately 102 KB of HTML; a fragment whose HTML exceeds 20 KB is flagged because combining fragments could push the total over the 100 KB limit.
- HTML and CSS size values are estimates computed at authoring time (a worst-case upper-bound); the actual size may differ at send time and is not the exact email a recipient receives.
- Size warnings are proactive signals, not hard blocks — they do not prevent sending and do not reflect the exact size recipients will see.
<script>and<base>tags are flagged as errors; meta refresh tags and empty divs are flagged as warnings.- CSS size is calculated from serialized content, not the live editing state; unsaved edits show a Stale check label, and saving refreshes the calculation.
Terminology:
- Canonical name: Content check — Acronym: n/a — variants: content checks, content check pane
- Synonyms: “one-click fix” = “Apply fix”
- Do not confuse: “Error” (Red, blocks/should be resolved before sending) ≠ “Warning” (Orange, may affect rendering in specific clients) ≠ “Info” (Blue, does not block sending)
- Do not confuse: “estimated size (authoring time)” ≠ “delivered size (send time)”
FAQ:
- Q: Where do I find content checks? — They are always available in the Email Designer; click the Issues icon in the right rail to open the Content check pane.
- Q: Do size warnings block me from sending? — No, they are proactive signals, not hard blocks; they do not reflect the exact size recipients will see.
- Q: Why does the size shown differ from what recipients receive? — The estimate is a worst-case upper bound; conditional content renders only the matching branch at send time, personalization tokens resolve shorter, and the Optimize HTML size option strips whitespace and comments at send time.
- Q: What is a Stale check label? — It appears when you make edits without saving, indicating a result (such as CSS size, calculated from serialized content) may no longer be accurate; save to refresh.
- Q: What are the three severity levels? — Error (Red), Warning (Orange), and Info (Blue).