I have a data cleaning scenario where I am trying to identify all contacts with a duplicate email address listed on another contact and merge the 2(or more)? Any way I can do this in mass?
There's no "out of the box" way to do this en masse. There are tools out there on the AppExchange that can do this for you, the Duplicate Rules feature can help you prevent duplicates, or you could build your own tool, such as a Batchable Apex class that sweeps over your database and merges duplicates. Just keep in mind that merging duplicates by email alone might not be preferable in all cases. Personally, I'd recommend that you go with an app if you don't have a lot of experience or time to build your own solution. This is something that's already been solved, and that you can leverage for a nominal cost.
I've been doing the same thing recently. Personally I've been exporting data with the data loader including id's - doing Vlookups in excel and tagging duplicates then when I update back into SF run a report on the duplicate tag so they say "Duplicate" in the company/contact name for example and then from there I can decide if I delete or merge etc. Sure there are faster ways but this was the easiest for me
Good luck with it :)