Using the preheader text

It is the line shown next to your subject in the inbox. Many people ignore it and throw away free space.

What shows by default

The first words of your message. Often "Not viewing this correctly?" — which is exactly the opposite of an argument.

What it should do

Complete your subject line, not repeat it. The subject makes the promise, the preheader gives the concrete detail.

Length

Around forty characters are visible on a phone. Put what matters at the start.

Do not leave it empty

An empty preheader pulls random text out of your template. An average line beats a technical fragment.

Test it

It is one of the few elements where a change measures directly on opens and clicks, without touching the message itself.