The double-opt-in-email, also called a registration or activation email, is the email that your recipient is sent when they subscribe to your newsletter, for example via the Newsletter2Go web form on your website.

This email is sent so that the recipient willingly confirms that they wish to receive the newsletter with the given email address in the future. For legal reasons it is therefore important that this email contains no advertising content.
In addition, it is recommended that you mention the details of the permission given, e.g. frequency, content topics and unsubscribing options etc., in order to make the conditions of the email reception transparent.