If you need to use the mailing lists in Plesk you first need to enable Mailman or the Mailing Lists Manager. Mailman is not enabled until you create a mailing list. For more information about creating mailing lists, see Adding a Mailing List in Parallels Plesk Panel.
Plesk does not verify the email addresses so make sure they are correct before creating the Mailing List.
If the Set Up Mailman icon is disabled, you need to install the latest Mailman updates. Select the Updater icon to install the Mailman updates.