Have you ever sent a newsletter campaign, checked GA4 the next morning, and found that none of the traffic landed under the Email channel? Or wondered why your SMS blast got bucketed into Referral instead of SMS?

If you ask five marketers what channel Email, SMS, and Mobile Push land in inside GA4, you will get five different guesses. "Probably Referral, or (other)?" is the most common answer.

But there is no guesswork involved. GA4 has an official Default Channel Group spec that decides exactly which of the 23 channels every visit gets classified into, based on the utm_source and utm_medium values. Google publishes the full logic, and operators cannot override it on the default report.

In this post, I decode the official Email, SMS, and Mobile Push judgement rules straight from the public documentation, so you stop guessing and start naming UTMs correctly on the first try.

TL;DR

• Email channel rule is satisfied when utm_medium=email (or three alternate spellings). The shortest correct form is utm_medium=email.
• SMS channel rule is an exact string match on sms. LINE, WhatsApp, and Messenger are NOT SMS — they fall into Referral or Organic Social.
• Mobile Push uses 3 OR conditions. Any one of utm_medium ending in push, containing mobile or notification, or utm_source=firebase triggers it.

1. What is the Default Channel Group, and who decides it

GA4's Default Channel Group is a system that classifies each visit by looking at the combination of utm_source and utm_medium and matching them against an official rule set. You cannot rename channels in the report UI. You can build a separate custom channel group, but the default 23-channel logic is locked down by Google.

The judgement logic lives in two official files:

• Channel definitions — the "[GA4] Default channel group" help page lists the condition expressions for all 23 channels.
• Source Categories table — a .xlsx file Google distributes with 819 entries, mapping each utm_source value to a category like SOCIAL, SEARCH, VIDEO, or SHOPPING.

This post focuses on the first file. The second one is covered in the sibling utm_source post I wrote separately.

Here is the full list of 23 channels GA4 currently defines. Email, SMS, and Mobile Push are the three most commonly misclassified despite being the ones operators design UTMs for most actively.

Why the default rules are locked

GA4 keeps the channel logic centralized so reports stay comparable across companies and industries. If every operator could redefine "Email" or "Referral" on their own report, no benchmark study, no GA4 official guide, and no third-party tutorial would work consistently. Custom channel groups exist precisely to handle company-specific views without polluting the shared 23-channel definition.

One common misconception is that channel classification is "GA4 trying to guess what the traffic is". It is not guessing — it is running a fixed rule set against your UTM values. If the rule does not match, the traffic falls into Unassigned. That is a UTM naming problem on the sender side, not a GA4 detection failure.

2. Email channel rule — which UTM values actually land in Email

Newsletter senders ask this every week. What exactly do you put in the UTM so that GA4 buckets the click into the Email channel? The official condition is:

Email — Source matches "email|e-mail|e_mail|e mail" OR Medium matches "email|e-mail|e_mail|e mail"

utm_source and utm_medium are joined by an OR, so satisfying either side is enough. Four spellings are accepted (email, e-mail, e_mail, e mail) — hyphen, underscore, and space variants all pass.

Three classic mistakes that knock Email out of the bucket

• utm_medium=newsletter — a direct translation of "newsletter" feels natural, but it is not in the 4 accepted spellings. It drops to Paid Other or (other).
• utm_medium=mail — the leading e is missing. Plain mail does not match the regex, so Email disappears from your channel report.
• utm_source=mailchimp with utm_medium left blank — Source side has no email substring, so the condition fails. Blank utm_medium is the single biggest cause of newsletter clicks falling into Referral.

If you want to keep utm_source as the ESP name (mailchimp, sendgrid, klaviyo) for internal segmentation, always pair it with utm_medium=email so the Medium side condition fires.

Recommended format and judgement cheat sheet

The recommended format for newsletter UTMs is:

utm_source=mailchimp     # the ESP / internal segmentation unit
utm_medium=email         # shortest of the 4 accepted spellings
utm_campaign=2026-05-launch
utm_content=cta-button-top

Here is how common utm_medium values get classified by GA4's Email rule on one chart.

3. SMS channel rule — and why LINE / WhatsApp do NOT count

The SMS channel rule is even simpler:

SMS — Source exactly matches "sms" OR Medium exactly matches "sms"

Unlike Email, this is an exact match. Any other spelling — including SMS with uppercase letters — fails. GA4 stores values case-sensitively, so utm_source=SMS will not match.

Is LINE / WhatsApp considered SMS? The official answer is "No"

It is tempting to lump every messaging channel together, but GA4's SMS definition only reacts to the literal string sms. Putting utm_source=line or utm_source=whatsapp will not trigger SMS classification — they land in Referral or Organic Social depending on the Source Categories table.

"We want to see LINE Official Account clicks alongside SMS as a messaging cluster" is a common request that the default channel group cannot satisfy. The practical workarounds are: (a) create a custom channel group, or (b) keep SMS as its own channel and track LINE separately inside Referral by filtering on utm_source=line.

Recommended format and judgement cheat sheet

Here is the recommended SMS UTM format and the values that pass or fail the SMS rule.

4. Display, Mobile Push, Affiliates, Audio — quick reference

Outside of Email and SMS, the channels where operators most often craft UTMs by hand are Display, Mobile Push, Affiliates, and Audio. Here is the official judgement rule for each one on a single reference chart.

Mobile Push is the most flexible — it has 3 OR conditions, so utm_medium=web-push, utm_medium=mobile-app, or utm_source=firebase all qualify independently. If you send from a web push notification tool, drop one of those into utm_medium and you are covered.

3 steps to check whether your own UTMs are misclassified

Once you know the spec, here is how to audit your own GA4 property:

1. Open Acquisition → Traffic acquisition and break down by "Default channel group".
2. Look at the last 30 days. If there is meaningful volume in "Unassigned" or "(other)", you have UTMs that do not match the official conditions.
3. Add Session source / medium as a secondary dimension and read the raw utm_source / utm_medium values to find the offending combinations.

If Unassigned plus (other) is over 5 percent of sessions, you almost certainly have inconsistent UTM naming across campaign owners.

5. Classifying correctly is step one. The real question is revenue.

Decoding the official spec is great, but what operators actually want to know is which channel is driving revenue. The 1,000 Email-classified sessions are interesting only when you can also see how many converted and what the average order value was. Without that, the channel report stays a vanity metric.

GA4 is built to measure the traffic side — sessions per channel. I'm building a tool called RevenueScope that approaches this from the opposite direction: revenue first, then trace back to the channel. It complements GA4 rather than replacing it. Once your UTMs are classified correctly inside GA4, the same values flow into RevenueScope and show up as Revenue Per Session (RPS) and Average Order Value (AOV) per channel — so Email, SMS, and Mobile Push contribution to the bottom line lives on one screen.

The point is: "classify correctly" is step one of two. Step two is connecting that classification to revenue per session. A channel report that ends at session count tells you what happened. A channel report that goes through to revenue tells you what to do next — which channel deserves more budget next month, and which one is wasting impressions despite high session volume.

Related posts on the same series:

• Meta Ads utm_source — what to actually put in (pillar: utm_source edition, official Source Categories)
• Meta Ads utm_medium — official regex guide (sibling: utm_medium edition)
• TikTok and LinkedIn utm_source — Google's official answer (sibling: per-platform utm_source edition)
• This article in Japanese

References

1. Google Analytics Help — [GA4] Default channel group (May 2026)
2. Google — GA4 Default Channel Group Source Categories (official .xlsx, 819 entries) (latest verified May 2026)

What does your team's UTM convention look like for Email and SMS? Are you seeing meaningful volume in Unassigned or (other) on the GA4 channel report? Drop a comment below — curious how others are handling the LINE / WhatsApp grey zone in particular.