How can I set a default retention policy to all new accounts created so they adopt the policy by default.

I have tried running...

Set-RetentionPolicy -Identity "Company Wide Retention Policy" -IsDefault $true

A parameter cannot be found that matches parameter name 'IsDefault'.
    + CategoryInfo          : InvalidArgument: (:) [Set-RetentionPolicy], ParameterBindingException
    + FullyQualifiedErrorId : NamedParameterNotFound,Set-RetentionPolicy
    + PSComputerName        : ex13mb01.mydomain.local

• Edited by BTRowdy1 12 hours 30 minutes ago

https://technet.microsoft.com/en-us/library/dn775046(v=exchg.150).aspx

I dont think you can do that. See the section:

Set another policy as the default retention policy to be applied automatically to new users

No

No"