Quick answer, create a template of user email and timestamp. Create a self relation to the data in the sheet using user email. Then create a single value column to get last email timestamp value. Finally use an if then column to compare template to single value. If it matches, it’s the last row.
Or you can incorporate rollup to get max date instead of single value from the relation. Then create a template of email and rollup and check if it matches the current row.
Finally filter by if then column result.