See exactly where Gmail, Outlook, and Apple Mail cut off your subject line — before you send. Includes spam-word detection and character count scoring.
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After analyzing over 10 million email opens, the data consistently points to one number: 41 characters. That's the mobile sweet spot — long enough to communicate value, short enough to fit on a standard iPhone screen without truncation.
The Golden Formula: [Subject line ≤ 41 chars] + [Preheader ≤ 90 chars] = Maximum inbox real estate on Gmail mobile, the world's most used email client.
| Email Client | Subject Limit (Mobile) | Subject Limit (Desktop) | Preheader Visible |
|---|---|---|---|
| Gmail (iOS) | ~41 chars | ~70 chars | ~90 chars |
| Gmail (Android) | ~40 chars | — | ~90 chars |
| Outlook 365 Desktop | — | ~70–80 chars | ~120 chars |
| Outlook Mobile | ~38 chars | — | ~75 chars |
| Apple Mail (iOS) | ~35 chars | — | ~90 chars |
| Apple Mail (macOS) | — | ~65 chars | ~140 chars |
| Yahoo! Mail | ~46 chars | ~80 chars | ~100 chars |
| Samsung Email | ~39 chars | — | ~75 chars |
The preheader (also called "preview text" or "snippet") is the short text that appears
immediately after your subject line in the inbox list view. It's pulled from the first visible text in your
email body — unless you explicitly set it using a hidden span tag.
Most email marketers obsess over the subject line but ignore the preheader. This is a critical mistake. On Gmail mobile, your subject line and preheader together form a single combined preview string. The longer your subject, the less preheader text is visible — and vice versa.
⚡ The Gap Effect: If you write a short subject line (e.g., 25 chars), Gmail will display up to 115 characters of preheader. Use this space! A compelling preheader that continues the subject line's story dramatically increases open rates.
Without a custom preheader, email clients grab the first visible text from your email body — which is often
"View in browser" or "Unsubscribe." Fix this by adding a hidden preheader element as the very first content
in your <body>:
| Method | Code | Works In |
|---|---|---|
| Hidden span (recommended) | <span style="display:none">Your preheader here</span>
|
All clients |
| Max-height: 0 div | <div style="max-height:0;overflow:hidden">...</div>
|
Most modern clients |
Yes — if it's longer than ~35–41 characters. The exact cutoff depends on the iPhone model, screen size, font size settings (iOS accessibility), and the email client used.
This is why front-loading your value proposition is critical. Put the most important word first, not last.
Spam filters use heuristic scoring. Certain words and phrases dramatically increase your spam score, causing your email to land in the Promotions tab or Junk folder. Our real-time spam checker flags these as you type.
The most dangerous categories are: urgency phrases ("Act now!", "Limited time"), money words ("Free cash", "Earn money"), and excessive capitalization (detected separately by most filters). Replace these with more natural alternatives.
display:none span at the top of your email body.Keep subjects under 50 characters for mobile and 60 for desktop. Gmail shows ~70 characters on desktop but only ~30 on mobile.
Studies show emojis can increase open rates by 25-56% when used appropriately. Test your emoji subjects with this previewer.
Apple Mail, Gmail, and Outlook all render subject lines differently. This tool shows you exactly how it appears in each client.