IMCAEX The recipient's e-mail address was not found in the recipient's e-mail system.

Check If your User have LegacyExchangeDN Attribute by using ADSIEDIT tool.





IF The Attribute has not been set then execute the Powershell command below;

Get-MailContact -OrganizationalUnit "OUNAME" -resultsize unlimited Where-Object { $_.legacyexchangedn -eq "" } Set-MailContact
Get-MailUser -OrganizationalUnit "OUNAME" -resultsize unlimited Where-Object { $_.legacyexchangedn -eq "" } Set-MailUser
Get-DistributionGroup -OrganizationalUnit "OUNAME" -resultsize unlimited Where-Object { $_.legacyexchangedn -eq "" } Set-DistributionGroup
Get-AddressList Set-AddressList
Get-AddressList Update-AddressList

Note: Instead OUNAME type your Organizational Unit name where your users resides.