What This Rule Detects

Identifies when utm_source indicates email traffic (mailchimp, newsletter, sendgrid, etc.) but utm_medium is NOT set to "email". This mismatch causes GA4 to misclassify email campaigns as Direct traffic because email clients strip referrers for privacy protection, and without utm_medium=email, GA4 cannot determine the traffic channel.

Why It Matters

Business Impact:

• Email campaigns invisible - Traffic appears as Direct instead of Email channel
• ROI calculation impossible - Cannot measure email marketing performance
• Budget allocation broken - Email success hidden, investment appears wasted
• Campaign optimization fails - Cannot A/B test or improve email strategies

Technical Impact:

• Gmail, Outlook, Yahoo, and Apple Mail strip HTTP referrer headers for user privacy
• GA4 sees no referrer when users click email links
• Without utm_medium=email, GA4 defaults to "Direct" channel classification
• Channel grouping logic specifically requires utm_medium=email for Email channel
• Result: 100% of email traffic misclassified as Direct

Real Example:

• Company sends 50,000 newsletter emails with utm_source=newsletter
• Links use utm_medium=referral (INCORRECT)
• Users click from Gmail, Outlook, Yahoo Mail
• GA4 sees: No referrer (email clients strip it)
• GA4 classification: Direct traffic (cannot detect email without medium)
• Report shows: 2,500 Direct sessions, 0 Email sessions
• Reality: All 2,500 sessions came from email, not direct
• Impact: Marketing team thinks email failed (0 sessions) while Direct traffic mysteriously spiked

Common Scenarios

Scenario 1: Email Source with Referral Medium

Using "referral" instead of "email" for newsletter campaigns:

Scenario 2: Mailchimp with Social Medium

Using incorrect medium for email platform:

Scenario 3: Email Platform with CPC Medium

Mixing paid advertising medium with email source:

How to Fix

Step 1: Understand Why Email Needs Special Handling

Email client privacy protection:

Email Client Behavior:
├── Gmail           → Strips HTTP referrer (privacy protection)
├── Outlook         → Strips HTTP referrer (privacy protection)
├── Yahoo Mail      → Strips HTTP referrer (privacy protection)
├── Apple Mail      → Strips HTTP referrer (privacy protection)
├── ProtonMail      → Strips HTTP referrer (privacy protection)
└── All others      → Generally strip referrer for user privacy

Result: GA4 receives ZERO referrer information from email clicks

Why utm_medium=email is critical:

1. Email clients don't send referrer data to destination websites
2. GA4 uses utm_medium to classify traffic into channels
3. Without utm_medium=email, GA4 cannot detect email traffic
4. Traffic defaults to "Direct" channel (no referrer + no UTM channel indicator)
5. Your email campaigns become completely invisible in reports

Step 2: Identify Misconfigured Email Campaigns

Search your GA4 data for email sources with wrong medium:

1. Reports → Acquisition → Traffic acquisition
2. Add secondary dimension: "Session source"
3. Filter for email-related sources:
   • newsletter, mailchimp, sendgrid, constant-contact
   • klaviyo, hubspot, activecampaign, brevo
   • Any source that represents email platforms
4. Check "Session medium" column
5. Look for anything OTHER than "email"

Common wrong medium values found:

❌ utm_medium=referral (should be email)
❌ utm_medium=link (should be email)
❌ utm_medium=newsletter (should be email)
❌ utm_medium=marketing (should be email)
❌ utm_medium=campaign (should be email)
❌ utm_medium=social (should be email)

Step 3: Update Email Platform Settings

Mailchimp:

1. Navigate to: Campaigns → Email
2. Select campaign → Edit → Settings
3. Find "Google Analytics link tracking"
4. Ensure utm_medium is set to: email
5. Do NOT use: referral, newsletter, or other values

SendGrid:

1. Settings → Tracking → Google Analytics
2. Set Default UTM Medium: email
3. Apply to all email templates
4. Verify in test emails before sending

Constant Contact:

1. Campaign settings → Tracking
2. Google Analytics: Enable
3. Medium field: email (lowercase)
4. Update all active campaigns

HubSpot:

1. Marketing → Email → Settings
2. Tracking & Analytics → Google Analytics
3. Default Medium: email
4. Apply to all email tools

Step 4: Fix Active Campaign Links

For campaigns you can edit:

1. Log into your email marketing platform
2. Find active/scheduled campaigns
3. Check all tracking links
4. Change utm_medium to "email" (lowercase)
5. Send test email to yourself
6. Click links and verify GA4 shows "Email" channel (use Real-Time reports)

For email signatures and automated emails:

1. Review all email signature links
2. Update transactional email templates
3. Fix automated drip campaign links
4. Update welcome email series
5. Verify every automated email has utm_medium=email

Step 5: Establish Email Tagging Standard

Create email campaign URL template:

# Email Campaign URL Structure
 
## Required Format
`{landing_page_url}`?utm_source=`{email_platform}`&utm_medium=email&utm_campaign=`{campaign_name}`
 
## utm_medium Rule
- ALWAYS use: email (lowercase)
- NEVER use: referral, newsletter, link, campaign, marketing
 
## Examples by Platform
 
### Newsletter (self-hosted)
utm_source=newsletter&utm_medium=email&utm_campaign=weekly-digest-2024
 
### Mailchimp
utm_source=mailchimp&utm_medium=email&utm_campaign=product-launch-jan
 
### SendGrid
utm_source=sendgrid&utm_medium=email&utm_campaign=welcome-series-day1
 
### Constant Contact
utm_source=constant-contact&utm_medium=email&utm_campaign=event-invite
 
### HubSpot
utm_source=hubspot&utm_medium=email&utm_campaign=lead-nurture-series
 
### Klaviyo
utm_source=klaviyo&utm_medium=email&utm_campaign=abandoned-cart

Examples

❌ Incorrect Examples

Newsletter with referral medium:
?utm_source=newsletter&utm_medium=referral&utm_campaign=weekly
Problem: Gmail strips referrer, GA4 sees no referrer + non-email medium
Impact: Traffic appears as Direct, not Email
Report shows: Direct channel (email campaign invisible)

Mailchimp with newsletter medium:
?utm_source=mailchimp&utm_medium=newsletter&utm_campaign=promo
Problem: utm_medium "newsletter" not recognized by GA4 channel grouping
Impact: Traffic classified as "Unassigned" channel
Report shows: Unassigned channel (cannot measure email performance)

SendGrid with marketing medium:
?utm_source=sendgrid&utm_medium=marketing&utm_campaign=flash-sale
Problem: "marketing" is not a GA4-recognized medium
Impact: Appears as Unassigned or Direct, breaks email attribution
Report shows: Cannot identify as email traffic

Email signature with link medium:
?utm_source=email-signature&utm_medium=link&utm_campaign=employee-outreach
Problem: "link" is not a valid medium, no referrer from email clients
Impact: All clicks appear as Direct traffic
Report shows: Direct channel (email signature effectiveness unknown)

✅ Correct Examples

Newsletter with email medium:
?utm_source=newsletter&utm_medium=email&utm_campaign=weekly-digest-2024
Result: GA4 correctly classifies as Email channel
Impact: Email performance visible in reports
Report shows: Email channel with measurable sessions and conversions

Mailchimp with email medium:
?utm_source=mailchimp&utm_medium=email&utm_campaign=product-launch-jan
Result: Properly attributed to Email channel
Impact: Can measure Mailchimp campaign effectiveness
Report shows: Email channel with conversion tracking

SendGrid transactional email:
?utm_source=sendgrid&utm_medium=email&utm_campaign=order-confirmation
Result: Even transactional emails tracked correctly
Impact: Understand post-purchase engagement
Report shows: Email channel includes all email types

Email signature with email medium:
?utm_source=email-signature&utm_medium=email&utm_campaign=team-outreach-2024
Result: Signature clicks tracked separately from campaigns
Impact: Measure organic team member referral effectiveness
Report shows: Email channel with source="email-signature" for segmentation

GA4 Impact Analysis

Channel Classification:

• Wrong medium → Direct or Unassigned channel (email invisible)
• Correct medium (email) → Email channel (proper attribution)
• Impact: Difference between seeing 0 email sessions vs actual email performance

Traffic Source Reports:

• Wrong medium → Email traffic scattered across Direct/Unassigned
• Correct medium → All email traffic consolidated in Email channel
• Impact: Accurate vs completely broken email attribution

Conversion Attribution:

• Wrong medium → Email conversions credited to Direct traffic
• Correct medium → Email campaigns get proper conversion credit
• Impact: Cannot measure email ROI vs clear email performance metrics

Real-Time Reports:

• Wrong medium → Email clicks show up with no channel information
• Correct medium → Real-time validation shows Email channel immediately
• Impact: Cannot test vs immediate feedback on tracking accuracy

Detection in UTMGuard

UTMGuard automatically detects email source / medium mismatches:

1. Scans all utm_source values for email-related terms
2. Identifies email platforms and newsletter indicators
3. Checks if utm_medium matches "email"
4. Flags mismatches where email source uses non-email medium
5. Reports affected sessions and provides specific fix recommendations

Audit Report Shows:

• Total sessions with email source mismatch
• Specific email platforms detected (mailchimp, newsletter, etc.)
• Current (wrong) medium values
• Recommended fix: Change utm_medium to "email"
• Impact: How many sessions are misclassified as Direct

Related Validation Rules

Frequently Asked Questions

Q: Why do email clients strip referrer information?

A: Email clients prioritize user privacy. When you click a link in an email, the client doesn't want to reveal to the destination website that you clicked from Gmail, Outlook, or Yahoo Mail. This protects your email address and email client from being tracked. All major email clients (Gmail, Outlook, Yahoo, Apple Mail, ProtonMail) strip referrer headers by default.

Q: Can I use utm_medium=newsletter instead of email?

A: No. GA4's Default Channel Grouping requires exactly utm_medium=email (lowercase) to classify traffic into the Email channel. Using "newsletter", "mail", or any other value will result in Unassigned channel classification. The word must be precisely "email".

Q: What if I use multiple email platforms - should utm_medium differ?

A: No. utm_medium should ALWAYS be "email" for all email platforms. Use utm_source to differentiate platforms: utm_source=mailchimp, utm_source=sendgrid, utm_source=newsletter. Medium identifies the channel (email), source identifies the specific platform.

Q: Do transactional emails need utm_medium=email too?

A: Yes, if you want to track them. Order confirmations, password resets, and account notifications should use utm_medium=email if you want to measure their traffic. However, many companies choose NOT to add UTM parameters to transactional emails to avoid overwriting marketing attribution.

Q: Why does some email traffic show up correctly without utm_medium=email?

A: If the email client sends referrer information (rare for modern clients) AND you have configured GA4's measurement protocol correctly, GA4 might detect it. However, this is unreliable. Most email clients strip referrers, so you must use utm_medium=email for consistent tracking.

Q: Can I fix historical data where email appeared as Direct?

A: No - historical GA4 data cannot be modified. However, fixing your UTM parameters now ensures all future email traffic is correctly attributed. You can also create custom segments or reports that use other signals (campaign names, landing pages) to estimate historical email traffic.

Q: What if my email platform automatically adds different utm_medium?

A: Change the platform's default settings. Every major email platform (Mailchimp, SendGrid, HubSpot, Constant Contact, Klaviyo) allows you to configure default UTM parameters. Find the Google Analytics integration settings and change the default medium to "email". Check the platform's documentation for specific instructions.

Q: Does this affect email open tracking?

A: No. Email open tracking (tracking pixel) is separate from link click tracking (UTM parameters). UTM parameters only affect what happens when someone clicks a link in your email. Open tracking is handled entirely within the email platform and doesn't involve GA4 or UTM parameters.

Q: Should email signature links use utm_medium=email?

A: Yes, if they're in emails. Any link that appears in an email message (campaigns, signatures, automated messages) should use utm_medium=email because all email clients strip referrers. This applies to employee email signatures, automated replies, and transactional messages.

External Resources

• GA4 Default Channel Grouping Rules
• Email Client Referrer Policies
• Google Campaign URL Builder
• UTM Parameter Best Practices
• Email Marketing Analytics Guide