Until now I was a happy Datloader.io user as it allowed me on a Mac to insert from CSV and have this wonderful auto mapping feature where a Lookup or Master Detail relation can be pointed to an external Id field.
But...I just reached Dataloader.ios limits. No csv files bigger than 50 MB and with more than 40 MB the Dataloader.io reports an App crash.
The only offline dataloader for Mac that is a little bit more enhanced than Lexiloader seems to be Jitterbit's free Dataloader.
But I have a hard time figuring out how to resolve a lookup relationship with external id fields instead. Is that possible? And how?