(Browse) on the right of the text box to access the Select People and Groups dialog box. For more information on this dialog box, see Select People and Group dialog box. Reflects the current release of Nintex for SharePoint 2016. For your version, please access assistance through the Help button in the product.
Sends customizable workflow notifications to users via email, SMS, or instant messaging.
Sets the primary users who will receive the customized notification. To search for users or groups, click (Browse) on the right of the text box to access the Select People and Groups dialog box. For more information on this dialog box, see Select People and Group dialog box.
Send individual notifications
The CC field sets read only users who will receive the notification. CC recipients are not able to respond to the tasks. To search for users or groups, click (Browse) on the right of the text box to access the Select People and Groups dialog box. For more information on this dialog box, see Select People and Group dialog box.
The BCC field sets read only users who will receive the email. BCC recipients are not able to respond to the tasks. Other users addressed in the email via the To, CC and BCC fields will not be able to see any addresses in the BCC field. To set the BCC field, enter the account name, or alternatively, select the address book icon for additional options.
The From field sets the user or domain group that will appear as the sender of the message. This setting applies to emails only. If no From user or domain group is specified, the From address configured in Global Settings will be used. To search for users or groups, click (Browse) on the right of the text box to access the Select People and Groups dialog box. For more information on this dialog box, see Select People and Group dialog box.
The priority of the notification. This is only applicable when using email notifications.
The Subject is the title of the notification being sent. You can manually specify the value or build the value dynamically at run time using 
(Insert Reference). The Subject field can be set within the list or library where the workflow is being used
If an email is sent it will appear as the header or title of the email.
If an Instant Message is being sent it will be pre-appended to the body of the notification.
Allows file attachments to be added to the notification. You can specify multiple URLs by separating each URL with a semicolon. You can also specify multiple URLs by referencing a collection variable.
Please note: Files will not be received by a user when SMS or IM is selected as the delivery method.
This sets the format of the email.
Selecting:
Rich Text enables italicize, bold, underline and indent information within the email using simple HTML styles provided by the SharePoint rich text tool bar.
Plain Text is simply the text without any stylized formatting.
The body of the notification will adapt depending on whether the Rich Text or Plain Text format is selected. Within the space provided enter the content for the notification as straight text, also available are Insert reference fields from within the workflow.
Specifies whether or not the configured message header and footer template should be used in this email notification. This option is only available when enabled by an administrator.
Delivery type is the method of delivering the notification to the selected users. Available delivery options; Email, User preference or Instant Message (if enable on the server). For information on User preference, please refer to the Configuring user preferences.