System.Net.Mail.SmtpPermission.AddPermission C# (CSharp) Method

        public void AddPermission(SmtpAccess access)
        {
            if (access > _access)
                _access = access;
        }

 public override IPermission CreatePermission()
 {
     SmtpPermission perm = null;
     if (Unrestricted)
     {
         perm = new SmtpPermission(PermissionState.Unrestricted);
     }
     else
     {
         perm = new SmtpPermission(PermissionState.None);
         if (_access != null)
         {
             if (string.Equals(_access, "Connect", StringComparison.OrdinalIgnoreCase))
             {
                 perm.AddPermission(SmtpAccess.Connect);
             }
             else if (string.Equals(_access, "ConnectToUnrestrictedPort", StringComparison.OrdinalIgnoreCase))
             {
                 perm.AddPermission(SmtpAccess.ConnectToUnrestrictedPort);
             }
             else if (string.Equals(_access, "None", StringComparison.OrdinalIgnoreCase))
             {
                 perm.AddPermission(SmtpAccess.None);
             }
             else
             {
                 throw new ArgumentException(SR.Format(SR.net_perm_invalid_val, strAccess, _access));
             }
         }
     }
     return perm;
 }