Ok, all plugins added by the client have now been deleted, but still no Mail data showing.
Tried the serialization fixer script, but no luck there either (though it cleaned up a lot of data in that column of the table!).
Just to clarify, in the database, the meta_keys for CF7 have an underscore in front of them:
_form _mail etc.
I only ask because I see some meta_keys do not have the underscore...