Does using all caps matter?

Yes, using all caps matters for spam filtering. Excessive capitalization is a heuristic signal that triggers rules in most filtering systems.

The impact scales with extent. A single emphasized word in caps is usually fine. A FULLY CAPITALIZED SUBJECT LINE adds significant points. Body content in all caps compounds the problem.

SpamAssassin specifically includes rules that calculate the ratio of uppercase to lowercase characters. Exceeding thresholds adds points that can push borderline messages into spam.

All caps also creates user experience problems. It is harder to read and feels aggressive. Recipients may report such messages as spam simply because the formatting feels offensive.

Shouting rarely persuades. Confident communication does not need volume to command attention.