Preview streams are optional and must be enabled in the your Encoder options when creating a release.
1) In the Encoder, click Create Release
2) After filling out Artist, Title, Marketing label and Owner, click next
3) In the Email template tab, make sure that an email template is chosen (or imported)
4) Then check “Include audio streaming preview link in email”
When checked, the completed release will show a button in the email
template that will link the recipient to the Preview streams page and
behind the scenes, a page will be generated with shortened
preview-length tracks for the release.
In the page itself, a button will prompt the viewer to view the full release in their Play MPE Player (mobile users will view the release in their app).