When you send an email, your recipients see your name, the subject line, and the pre-header text.
The pre-header text is also called Johnson Box: the term commonly found at the top of direct mail letters, containing the key message of the letter. The purpose of pre-header is to draw the reader’s attention to this key message first and hopefully grab their attention, enticing them to read the rest of the letter.
So it is important to choose good pre-header text so recipients are more likely to open your campaigns.
You can change your preheader text in the email designer: