I don't know why this parameter can't be found, but for some reason when using the example from David Wyatt on the Technet Gallery Powershell is kicking back the error:
Send-MailMessage : A parameter cannot be found that matches parameter name 'InlineAttachments'.
I'm not using an old Powershell version or server, it is on a Windows Server 2012 R2 with PS versions of:
PS SQLSERVER:\> $PSVersionTable
Name Value
---- -----
PSVersion 4.0
WSManStackVersion 3.0
SerializationVersion 1.1.0.1
CLRVersion 4.0.30319.42000
BuildVersion 6.3.9600.17090
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0}
PSRemotingProtocolVersion 2.2
You need to download and install the Send-MailMessage cmdlet from the TechNet link you provided. The native version of Send-MailMessage does not have the InlineAttachments parameter.