Did you try makemap -u hash igusers.db? On some systems, it will dump out the contents of the database. Also, check that the file is a Berkeley DB database and that the version of the library is the same. The file format has changed with newer versions. From the sendmail maps that I looked at, they are standard key to value maps with no binary format.

Your first code shouldn't work. $val2 isn't defined anywhere but I bet that is a typo in your posting. The second won't work because $val isn't a reference. Even if it was a reference, ref doesn't dereference it, it returns the type.