# Tracking & UTM codes in Letterhead

## In this article we define Letterhead specific tracking codes to report on links clicked.

When you add a URL to your newsletter, regardless of the block used, we "wrap" it with additional information for tracking purposes.  Please review this example depicting how Letterhead attaches tracking codes for email tracking and metrics reporting.

**Original Link:**

[https://www.nytimes.com/2023/09/08/nyregion/donald-trump-civil-trial-date.html](https://www.nytimes.com/2023/09/08/nyregion/donald-trump-civil-trial-date.html)

becomes:

**[https://a.post.lhd.link/muysif0rhq/?lh\_aid=3584680&lh\_cid=h10t1yw8qa](https://link.whereby.us/muysif0rhq/?lh_aid=3584680&lh_cid=h10t1yw8qa)**

When a subscriber follows the updated link above, it takes them to: **[https://www.nytimes.com/2023/09/08/nyregion/donald-trump-civil-trial-date.html?lh\_aid=3584680&lh\_cid=h10t1yw8qa&di=019e0b2d1b84ebc5ce0b6d2e8278d55e](https://www.nytimes.com/2023/09/08/nyregion/donald-trump-civil-trial-date.html?lh_aid=3584680&lh_cid=h10t1yw8qa&di=019e0b2d1b84ebc5ce0b6d2e8278d55e)**

Below we explain our tracking codes:

- **lh\_aid** is the user hash. It's unique per subscriber.
- **lh\_cid** is a campaign id.
- **di** is a unique hash based on ip address and time of day.
- **lh\_em** (not in my example) will be the subscriber's email address if it's a link back to their website.

We **don't use utm** because we see that as a reserved word that users may want to use themselves. For example, if we used **utm\_source**, instead of **lh\_cid**, then a user wouldn't be able to set their own utm\_source.