I hit this every month: some ‘smart’ field turns 02139 into 2139 when exporting from Salesforce, and then ZIPs in New England blow up dedupe rules. Anyone else keep a quick fix handy besides forcing the column to Text on every import?
I stopped fighting Excel and saved a tiny Power Query that imports the CSV, forces ZIP to Text, and pads to 5 so ‘02139’ stays intact; now I just drop the monthly Salesforce export in the same folder and hit Refresh. Are you exporting a report or Data Loader — can tweak either way if needed.