What is line length limit in an email body?
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Email has a line length limit, and it matters more than you'd think. RFC 5322 (the spec that defines email format) says lines should be 78 characters or less, and must never exceed 998 characters. Go past 998 and mail servers will either fold your line (insert a line break mid-sentence) or reject the message entirely.
The 78-character guideline comes from ancient terminal displays that showed 80 columns. Email was designed to leave two characters for quote markers or line-ending sequences. The 998-character hard limit exists because early mail servers couldn't handle longer lines without breaking.
This breaks real emails in two common ways. First, if you're hand-coding HTML emails with long unbroken lines (think a massive <style> block with no line breaks), some servers will fold those lines mid-tag. Your CSS breaks, your layout collapses. Second, long URLs without breaks get folded mid-link. The URL splits across two lines, and suddenly your "Click here to reset your password" link 404s.
Most modern ESPs handle this automatically. Mailchimp, Brevo, Postmark, and others insert line breaks where needed before sending. But if you're sending raw SMTP (custom mail server, scripted sends, API calls to AWS SES or Mailgun without their SDKs), you're responsible for line length yourself.
If you're hitting this issue, it's usually because you're building email programmatically without proper encoding. The fix: use quoted-printable or base64 encoding for your email body. Both formats insert line breaks automatically and tell receiving servers how to reconstruct the original content. Most email libraries (like Python's email module or PHP's PHPMailer) handle this if you set the encoding correctly.
Worth checking if you're debugging broken links or mangled HTML. View the raw source of a sent email and look for lines longer than 998 characters. If you see any, your sending setup isn't folding lines properly. Our Source Analyzer can show you the raw MIME structure if you're stuck.
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