Freeform Checkbox Group Field only returns one value
Ok, Solspace support cam through via email with the answer...  Put square brackets after the field name!  Simple :)

&lt;input type="checkbox" name="MyFieldName[]" value="Item1"&gt;
&lt;input type="checkbox" name="MyFieldName[]" value="Item2"&gt;
&lt;input type="checkbox" name="MyFieldName[]" value="Item3"&gt;