https://www.alitajran.com/send-from-alias/
PS C:\Users\xx> Connect-ExchangeOnline
PS C:\Users\xx> Get-OrganizationConfig | ft Name, SendFromAliasEnabled
PS C:\Users\xx> Set-OrganizationConfig -SendFromAliasEnabled $True
PS C:\Users\xx> Get-OrganizationConfig | ft Name, SendFromAliasEnabled