Select a template you want to edit and in the template editor, click the "Template settings" button. Here you can edit default subject line, preheader and plain text version of this email template.
A subject line is a part of an email that users see first when it lands in their inbox. Try to keep it clear and descriptive. The subject line can be overwritten when making an API call.
A preheader is a summary text of your email. It follows the subject line when an email is viewed in the inbox. It’s not required to create a preheader but strongly recommended - it can save you some misunderstandings and email complaints.
Sidemail sends a plain-text version of your email template along with the HTML version. The text-only version is used in cases when a user’s email client does not support HTML messages or if a user prefers it.
The plain-text version is either auto-generated from your content elements: text, list and button or you can set your own. To set your own, turn off the Auto-generate plain-text version switch. The plain-text version cannot be empty.