diff --git a/.gitignore b/.gitignore
index b375c13..336fd7f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -28,4 +28,8 @@ lib/
 .eslintcache
 
 # Misc
-.DS_Store
\ No newline at end of file
+.DS_Store
+
+# Local datasets
+csvs
+old_csvs
\ No newline at end of file
diff --git a/README.md b/README.md
index cb49995..5311f3b 100644
--- a/README.md
+++ b/README.md
@@ -64,7 +64,7 @@ If you are on a GHEC instance (including EMU), please head to `https://github.co
     DIRECTORY_OF_CSV_CONTENT=XXX
     ```
 
-3.  Run the script
+3.  Run the script to deduplicate by username
 
     ```bash
     npm run start
@@ -75,3 +75,15 @@ The above script should output something like:
 ```
 You have a total of XX unique developers across your GitHub instances.
 ```
+
+If you want to deduplicate by email (to catch users with multiple usernames), run:
+
+```bash
+npm run email
+```
+
+The email deduplication script should output something like:
+
+```
+You have a total of XX unique developers (by email) across your GitHub instances.
+```
diff --git a/package.json b/package.json
index 3606f03..0193a97 100644
--- a/package.json
+++ b/package.json
@@ -25,6 +25,7 @@
   },
   "scripts": {
     "start": "npm run build && node lib/src/main.js",
+    "email": "npm run build && node lib/src/main-email-dedup.js",
     "clean": "rimraf coverage lib tmp",
     "prebuild": "npm run lint",
     "build": "tsc -p tsconfig.json",
diff --git a/src/main-email-dedup.ts b/src/main-email-dedup.ts
new file mode 100644
index 0000000..4e12dcf
--- /dev/null
+++ b/src/main-email-dedup.ts
@@ -0,0 +1,62 @@
+import { readdirSync, readFileSync } from 'fs';
+import { extname } from 'path';
+import { parse, ParseResult } from 'papaparse';
+import * as dotenv from 'dotenv';
+dotenv.config({ path: '.env' });
+
+const GLOBAL_DIRECTORY = process.env.DIRECTORY_OF_CSV_CONTENT || '';
+
+// Extended type to include email field (email might be optional)
+type CSVDataWithEmail = {
+  'User login': string;
+  'Organization / repository': string;
+  'Last pushed date': string;
+  'Last pushed email'?: string;
+};
+
+export const getFilesInDirectory = async (folder: string) =>
+  <string[]>readdirSync(folder).map((file) => file);
+
+export const filerByFileExtention = async (files: string[], format: string) =>
+  <string[]>files.filter((file) => extname(file).toLowerCase() === format);
+
+export const readMultipleFiles = async (files: string[]) =>
+  <string[]>(
+    files.map((file) =>
+      readFileSync(`${GLOBAL_DIRECTORY}${file}`, { encoding: 'utf8' }),
+    )
+  );
+
+export const convertContentToJSON = async (files: string[]) =>
+  files.map((file) => parse<CSVDataWithEmail>(file, { header: true }));
+
+export const mergeFileContent = async (data: ParseResult<CSVDataWithEmail>[]) => {
+  const mergedData: CSVDataWithEmail[] = [];
+  data.forEach((file) => {
+    mergedData.push(...file.data);
+  });
+  return mergedData;
+};
+
+export const uniqueUsersByEmail = async (data: CSVDataWithEmail[]) =>
+  <string[]>(
+    data
+      .map((user) => user['Last pushed email'])
+      .filter((email): email is string => email != null && typeof email === 'string' && email.trim() !== '') // Type guard to filter out undefined, null, or empty emails
+      .map((email) => email.toLowerCase())
+      .filter((email, index, arr) => arr.indexOf(email) === index)
+  );
+
+const run = async () => {
+  const files = await getFilesInDirectory(GLOBAL_DIRECTORY);
+  const csvFilesFound = await filerByFileExtention(files, '.csv');
+  const csvFiles = await readMultipleFiles(csvFilesFound);
+  const jsonFiles = await convertContentToJSON(csvFiles);
+  const content = await mergeFileContent(jsonFiles);
+  const unique = await uniqueUsersByEmail(content);
+  console.log(
+    `You have a total of ${unique.length} unique developers (by email) across your GitHub instances.`,
+  );
+};
+
+run();