Check Email Aliases

Prerequesite: Connect to Azure AD

The uppercase SMTP address is the primary address, while lowercase smtp are aliases. You can find the value in active directory in "User > Attribute Editor > proxyAddresses".

Get-AzureADUser -ObjectId "[email protected]" | Select -Property ProxyAddresses

Example Output

smtp:alias@domain.com
smtp:alias@domain.onmicrosoft.com
SMTP:primaryaddress@domain.com