How to Add New Lookup Domains into Windows DNS Suffixes

Error message:

[server005.intranet.kimconnect.com]: PS E:\Users\kimconnect\Documents> add-localgroupmember -Group 'remote desktop users' -Member 'DMZ/testUser'
add-localgroupmember : Principal DMZ/testUser was not found.
+ CategoryInfo : ObjectNotFound: (WBMD/SVasmatkar:String) [Add-LocalGroupMember], PrincipalNotFoundException
+ FullyQualifiedErrorId : PrincipalNotFound,Microsoft.PowerShell.Commands.AddLocalGroupMemberCommand

# Resolution: Add Entries to DNS Suffixes

$addDomains='dmz.kimconnect.com'
$currentList=(Get-DnsClientGlobalSetting).SuffixSearchList
$newList=@($addDomains)
$newList+=$currentList
Set-DnsClientGlobalSetting -SuffixSearchList $newList

# Use legacy command to add user into local group (in case Windoze OS is dinosaur)

net localgroup 'remote desktop users' DMZ/testUser /add