One issue you have is that you're adding a level of indirection by passing a reference to $names to validateNames, but it's already a reference (to the %data hash). So just call &validateNames($names).

As for printing the data, you can do this:

for my $key (keys %$valid_names) {
  print "key: $key\n";
  print "  name: $valid_names->{$key}{name}\n";
  print "  email: $valid_names->{$key}{email}\n";
}
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Finally, the places to look for more information on data structures and references are: perldata, perldsc, and perlref.