Email Addresses by Permission Set

email_perm_set.cls

// Get list of email addresses by Permission Set
public static List<String> getEmailByPermSet(String permsetname){
    List<Id> just_ids = new List<Id>();
    List<PermissionSetAssignment> users = [
        SELECT AssigneeId 
        FROM PermissionSetAssignment 
        WHERE PermissionSet.Name = :permsetname
    ];
    for(PermissionSetAssignment uid: users){
        just_ids.add(uid.AssigneeId);
    }

    List<String> just_email = new List<String>();
    List<User> email_list = [SELECT Email FROM User WHERE User.Id IN :just_ids];
    for(User usr: email_list){
        just_email.add(usr.Email);
    }

    return just_email;
}