Alan
Though not an expert, I've created a few forms with the Submit by Email button. If you've already done this then sorry for asking, but did you go through the Acrobat Distribution (Forms>Distribute Forms)process after creating the form in LC8? As far as I can tell the email submit button doesn't work without this stage.
This confirms the email submission address, then sets up a dataset to be saved in a location of your choice.
filename_dataset_0001.pdf
then a file type that can be edited, saved and submitted by Reader users:
filename_pub_0001.pdf
You can save this to your intranet server or email direct to the recipient.
When the submit button is then used you receive a copy of the whole form which on opening will prompt you to add it to the dataset. Receiving and adding multiple forms to the data set is straightforward. You will see them all listed in the viewer above the form itself. From here you can also then select and export the data to Excel via xml or as a csv file.
Note that any changes you make to the form should be to the original document and the distribution process repeated, otherwise the functionality of the form will be affected.
That's about the limit of my knowledge I'm afraid, therefore if you have already tried this and are still having problems then hopefully someone else can help out.
Regards