Well, the restriction here is that you're storing stuff in an underlying DBM database, so you're stuck with one value per key. That's why you need to do join/split or whatever tricks.

Otherwise, one would use a hash of hashes to store this information (as it's easier to search for stuff in a hash, so it makes sense to store the email addresses themselves in hashes as well). You could store something like this in DBM, but they you would be looking at bronto's suggestion of using serialisation techniques to flatten the data structure before storing it.

CU
Robartes-