How does message length impact spam filtering?

Message length has nuanced effects on filtering. Very short emails (just a link, minimal text) look suspicious—legitimate senders usually have something to say. Very long emails may trigger scrutiny simply because there's more content to evaluate, though length alone isn't penalized. The sweet spot is enough content to seem legitimate while respecting recipient attention.

More important than length is the text-to-image ratio and text-to-link ratio. Image-heavy emails with little text appear spammy. Emails stuffed with links relative to text trigger suspicion. A healthy email has substantive text content, reasonable image usage, and purposeful links—not padding to hit a word count.

Write what needs to be written. Don't artificially inflate emails to avoid "too short" filters, and don't pad with filler text. Focus on value: say what you need to say, no more, no less. If your email is genuinely short (a reminder, a notification), that's fine—context matters. A transactional email can be brief; a newsletter probably shouldn't be two sentences.