This may be off-topic, but i feel this is the best possible forum for finding a solution:
Using the 3rd party app "Campaign Monitor" is it possible to mass add leads (or contacts) to Campaign Monitor within salesforce without having to export the list of leads to a file and upload that way.
Attribution to: Bart
This content is remixed from stackoverflow or stackexchange. Please visit https://salesforce.stackexchange.com/questions/34762