What UTM tags do
UTM tags are small labels added to a link (utm_source, utm_medium, utm_campaign…) that tell Google Analytics where a visit came from. Without them, visits from emails, PDFs, QR codes and many apps show up as Direct, and you can't tell which campaign worked.
Get the channel right
GA4 sorts visits into channels like Email, Organic Social, Paid Search or Referral using the source and medium. A medium it doesn't recognize ends up as Unassigned. This builder shows the channel GA4 will use, so you can fix it before the link goes out.
Keep everything lowercase and use the same words every time: GA4 treats "Email" and "email" as different values, which splits your reports.