External chat disabled after s4b onpremise to teams migration

Finally Teams users with license are able to chat with external users.

Thanks to all AndresGorzelany Holger_Bunkradt adam deltinger StaleHansen 

Issue :

Skype 4 business On premise shutdown and We have few users with teams license.

Those users with teams license were not able to chat with external users and below message was shown :

 "chat is disabled , This user is currently using Skype for Business".

Steps :

1. Updated DNS to Online DNS

https://docs.microsoft.com/en-us/skypeforbusiness/hybrid/decommission-manage-dns-entries

      2. Cleared all msRTCSip- attributes in Local AD

https://www.linkedin.com/pulse/sfb-on-prem-decommission-interpretedusertype-andres-gorzelany/

https://msunified.net/2019/07/11/my-post-migration-from-skype-to-teams-toolbox/

Before clear : 

msRTCSIP-DeploymentLocator: SRV

After Clear :

msRTCSIP-DeploymentLocator: 

#select users for clearing attributes  
$users=Get-ADuser 
foreach($user in $users){ 
$u=$user.UserPrincipalName 
#Get All msRTCSIP properties for a user that has a value 
$Properties=Get-ADuser -Filter {UserPrincipalName -eq  $u} -Properties * | Select-Object -Property 'msRTCSIP*' 
if($Properties -match "srv"){ 
    #clear all properties for a user 
     Get-ADuser -Filter {UserPrincipalName -eq  $u} -Properties * |Set-ADUser -Clear ($Properties | Get-Member -MemberType "NoteProperty "| % {$_.Name}) 
 $properties 
}}

3.Updated Coexistence Mode in Teams Admin Center to TEAMSONLY

https://admin.teams.microsoft.com/company-wide-settings/teams-upgrade

4. Used Latest Azure ad connect to Sync users with Online AD

Enabled Attribute synchronization for lync server and followed below article for recommended.

https://docs.microsoft.com/en-us/azure/active-directory/hybrid/reference-connect-sync-attributes-synchronized

Shown some errors during sync:

https://www.petenetlive.com/KB/Article/0001638

#Manualy Sync AD : 
Start-ADSyncSyncCycle -PolicyType delta 

5.Check Online user attribute 

#If MicrosoftTeams Module is Not installed
Install-Module MicrosoftTeams

#Import Microsoft teams
Import-Module MicrosoftTeams 

$userCredential = Get-Credential 
Connect-MicrosoftTeams -Credential $userCredential 

#Gets all users 
#Get-CsOnlineUser 

#Gets all Properties for Single user 
$user='abc@domain.com'

#Get-CsOnlineUser $user

#Gets all Properties related to Teams
Get-CsOnlineUser $user | Format-List UserPrincipalName, DisplayName, SipAddress, Enabled, TeamsUpgradeEffectiveMode, EnterpriseVoiceEnabled, HostedVoiceMail, City, UsageLocation, DialPlan, 
TenantDialPlan, OnlineVoiceRoutingPolicy,LineURI, OnPremLineURI, OnlineDialinConferencingPolicy, TeamsVideoInteropServicePolicy, TeamsCallingPolicy, HostingProvider,
InterpretedUserType, VoicePolicy, CountryOrRegionDisplayName

6. InterpretedUserType and HostingProvider are the main properties

Before sync:

After Sync

# Get current Teams federation settings before change. 
Write-Verbose -Verbose -Message "Before change:" 
Get-CsTenantFederationConfiguration 

# Disable communication with accounts on public IM and presence providers such as Windows Live, Yahoo, and AOL. 
Set-CsTenantFederationConfiguration -AllowPublicUsers $false 

# Enable Teams federation. 
Set-CsTenantFederationConfiguration -AllowFederatedUsers $true 

  
# Run for Add Multiple domain 
# Function to add allowed domain for Teams federation. 

function Enable-TeamsFederationForAllowedDomainsOnly { 
param ( 
 [parameter(Mandatory = $true)] 
 [string[]]$AllowedDomains, 
[parameter(Mandatory = $false)] 
 [switch]$RemoveExistingDomains 
 ) 
  # Remove existing domains (if requested). 
 if ($RemoveExistingDomains) { 
   Write-Verbose -Verbose -Message "Removing existing domains..." 
  Set-CsTenantFederationConfiguration -AllowedDomainsAsAList $null 
 } 
 # Add each domain to the list of allowed domains. 
 foreach ($Domain in $AllowedDomains) { 
 Write-Verbose -Verbose -Message "Adding $Domain..." 
Set-CsTenantFederationConfiguration -AllowedDomainsAsAList @{Add=$Domain} 
 } 
} 

# List of domain to allow. 
$AllowedDomains = "domain1.com", 
"domain2.com", 
"domain3.com" 

# Set Teams federation settings to allowed domains only. 
Enable-TeamsFederationForAllowedDomainsOnly -AllowedDomains $AllowedDomains -RemoveExistingDomains 

# Get current Teams federation settings after change. 
Write-Verbose -Verbose -Message "After change:" 
Get-CsTenantFederationConfiguration

$x = New-CsEdgeAllowAllKnownDomains 
Set-CsTenantFederationConfiguration -AllowedDomainsAsAList $x 
Get-CsTenantFederationConfiguration 

Now External chat is working !!!!!

Please do comment to add more into this thread.