Does using ALL CAPS trigger spam filters?

Excessive ALL CAPS can contribute to spam scores, particularly in subject lines and prominent content areas. This pattern is associated with aggressive spam tactics and triggers heuristic rules in many filters.

The impact depends on extent and context. A single capitalized word for emphasis is usually fine. AN ENTIRE SUBJECT LINE IN CAPS raises flags. Combined with other spam indicators, caps can push a message over the threshold.

SpamAssassin includes rules that specifically target excessive capitalization. These rules check the ratio of uppercase to lowercase characters and add points when the balance tilts toward shouting.

Beyond spam filtering, all caps reduces readability and makes messages feel aggressive. Even if filters allowed it, recipients respond poorly to content that appears to shout at them.

A ship flying distress signals when there is no emergency draws unwanted attention. Use emphasis judiciously.