Upload list to Marketo with existing members - Duplicate or Update?

[Darshil_Shah1 · Accepted solution]

@ayaspan, Do you by any chance have custom dedupe criteria (e.g., email address + other field/partition ID, etc.) enabled in your instance (especially for the list import as an input source)?

[ayaspan]

This turned out to be correct. Apparently a while ago IT thought this would be a good idea. Mystery solved.