A Suppression list is a list where you should include the members of your list that you never want to be added to it again and to never send them any of your future newsletters. Keep in mind that, after moving said members to this list, you won't be able to ever add them to any of your mailing lists in the future.
Now let's see how you can find the Suppression list:
1. Click on the Mailing Lists button, located on the left side of your Moosend account.
2. Click on the Settings icon on the right top corner of your mailing lists page and then choose the Suppression List option on the menu appearing.
Once inside your Suppression List, you can view all the members contained in it.