Tracking & UTM codes in Letterhead

When you add a URL to your newsletter, regardless of the block used, we “wrap” it with additional information for tracking purposes. This is how Letterhead reports clicks and engagement metrics. Here’s an example of how a link is transformed:

Original link:

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

becomes a wrapped tracking link:

https://a.post.lhd.link/muysif0rhq/?lh_aid=3584680&lh_cid=h10t1yw8qa

When a subscriber follows the wrapped link, it takes them to the original destination with tracking parameters appended:

https://www.nytimes.com/2023/09/08/nyregion/donald-trump-civil-trial-date.html?lh_aid=3584680&lh_cid=h10t1yw8qa&di=019e0b2d1b84ebc5ce0b6d2e8278d55e

What each tracking code means

• lh_aid — the user hash. It’s unique per subscriber.
• lh_cid — a campaign id.
• di — a unique hash based on IP address and time of day.
• lh_em — (not in the example above) the subscriber’s email address, included when the link points back to your own website.

Why we don’t use UTM parameters

We don’t use utm parameters because we treat those as reserved for you. For example, if we used utm_source instead of lh_cid, you wouldn’t be able to set your own utm_source. You can add your own UTM codes to newsletter links — see Working in Emails.

Curious why some antivirus tools flag wrapped links? See Why does my antivirus give me a warning?