Short answer
Both LinkedIn and Google match hashed email lists, but they normalise slightly differently. LinkedIn: lowercase, remove all whitespace, then SHA-256. Google: lowercase, remove spaces and, for gmail.com and googlemail.com addresses, remove dots before the @, then SHA-256 in hex. LinkedIn's API lists 10,000 rows as the minimum for contact list uploads and needs 300 matched members to serve. Hashing protects the file in transit; it doesn't make the data anonymous.
Normalisation by platform
| Step | LinkedIn contact list | Google Customer Match |
|---|---|---|
| Case | Lowercase | Lowercase |
| Spaces | Remove all whitespace | Remove spaces before, after and inside |
| Gmail dots | Keep | Remove dots before @ for gmail.com and googlemail.com |
| Hash | SHA-256 (required for API uploads) | SHA-256, hex |
| Header | ||
| File | CSV, UTF-8 recommended | CSV, UTF-8 or ASCII |
The SHA-256 email hasher applies either set of rules in your browser and outputs an upload-ready CSV.
Size rules
- LinkedIn: the API documentation lists 10,000 rows minimum and 300,000 maximum per contact list, and an audience needs 300 matched members to serve.
- Google: match rates are reported for uploads with at least 100 rows matched to users; check the current serving thresholds in your account.
Why B2B lists match poorly
Ad platforms match the email a person signed up with. Many professionals use a personal address for LinkedIn and Google, so a CRM full of work emails often matches less than a consumer list would. Three fixes, in order:
- Add a company list targeting the same accounts. Clean it first.
- Include extra identifiers where the platform accepts them, such as first name, last name, company and country on LinkedIn.
- Use contact lists mainly for exclusions (customers, staff) and retargeting known prospects.
Privacy still applies
- A SHA-256 hash of a known address can be recreated by anyone who has the address, so hashed lists remain personal data.
- Upload only data you have a legal basis to use for advertising, and record it.
- Hash on your own device, upload, then delete the working file. More on the legal side.
Questions
Do I have to hash emails myself?
For LinkedIn's API, emails must be SHA-256 hashed before upload. Google accepts hashed or plain data in its interface and hashes plain data itself; hashing first keeps raw addresses off the upload.
Why is my B2B match rate low?
Platforms match on the email a member signed up with, often a personal one. Work emails match less often, so add a company list alongside contact lists.
Is a hashed email still personal data?
Treat it as personal data. A hash of a known address can be recreated, so it identifies a person to anyone holding the same address.
What headers do the files need?
LinkedIn contact lists use email (plus optional firstname, lastname, employeecompany, title, country). Google Customer Match uses English headers such as Email, Phone, First Name, Last Name, Country and Zip.
Facts checked against the sources below on 19 October 2026. Ad platforms change quickly: if something here no longer matches what you see, tell us and we will update it.
