Mailchimp UTM tracking: the checkbox or your own tags
Mailchimp can tag your email links for you: tick Google Analytics link tracking in the email's Settings & Tracking section. To choose the values yourself, build them here with utm_medium=email and leave that box unticked. Mailchimp's help says running its tracking and your own UTMs on the same links can skew your reports.
The interactive UTM builder loads with this page, pre-filled for Mailchimp, and runs entirely in your browser.
GA4 files a click under Email when the medium is email, as long as the source isn't one of the social, search, video or shopping sites on Google's list, so utm_source can name Mailchimp and keep these sends apart from any other tool that emails your list.
Where to put it
Regular email: in the email builder's Settings & Tracking section, tick Google Analytics link tracking and save. To use your own tags instead, leave it unticked and paste the tagged URLs as your link targets.
Automation flows: click Edit Settings on the flow and tick the same box. To change one email's values, open that email action's three-dot menu and choose Modify UTM Parameters.
In Modify UTM Parameters, fill in every field. Mailchimp won't accept a blank one, and Reset Defaults brings its original values back.
A/B tests: the checkbox is under Tracking on the Setup step.
Hand-tagged links: make sure nothing follows the URL in the link field, not even a space. Mailchimp's troubleshooting list says Google Analytics won't work with a trailing space.
One Mailchimp email type refuses the Google Analytics checkbox outright: the single welcome email in classic automations. Every other classic automation email accepts it, so for most emails the choice is whether the checkbox tags your links or you do. Pick one per email, as Mailchimp's troubleshooting notes advise.
What the checkbox gives you. Tick it and Mailchimp shows the title the email will carry in Analytics: the email's title plus the send date. What it doesn't give you is a published list of values. Mailchimp's help page describes the fields but never states the source, medium or campaign it writes by default. If you need to be certain clicks reach GA4's Email channel, read the medium in Modify UTM Parameters on a flow email, or tag the links yourself with utm_medium=email. When you edit a title, Mailchimp warns that special characters can break your URLs.
A/B tests report under one title. For an A/B test, the Analytics title joins the test title, the date and the Campaign ID, and every combination shares it. Mailchimp gives each content combination its own web ID and says to write them down before sending: preview each version, copy the unsubscribe link, and note the value after c=. If you'd rather see versions split in GA4 itself, leave the checkbox off for that test and give each version's links a different utm_content.
The numbers live in GA4 now. Since the switch to Google Analytics 4, Mailchimp says statistics for tracked emails and flows can only be viewed in your Analytics account, not in Mailchimp. Set Analytics up before you send, too. Mailchimp is blunt that it can't track retroactively.
Tags need a page to land on. A UTM is read by the Analytics code on the page it opens. Link straight to a PDF or an image and Mailchimp says you may need custom tracking on your server; linking to a page that holds the file is simpler. Mailchimp also says Analytics won't track a redirect that doesn't carry the Analytics code, and recommends direct links. Run anything that redirects through the redirect checker to see where it really lands. For naming lists and sends, the email UTM builder has the conventions.
Questions
Does Mailchimp add UTM parameters automatically?
Only once you turn it on. Tick Google Analytics link tracking in a regular email's Settings & Tracking section, on a flow's Edit Settings, or under Tracking in an A/B test's Setup step, and Mailchimp tags the links. Leave it off and tagging is up to you.
Can I use my own UTM parameters with Mailchimp's Google Analytics tracking?
Mailchimp recommends choosing one. Its troubleshooting notes say combining its Google Analytics tracking with custom UTM tracking could skew your reports. If you hand-tag an email's links, leave the checkbox unticked for that email.
Why can't I see Google Analytics results inside Mailchimp?
Since the move to GA4, Mailchimp shows statistics for GA-tracked emails and flows only in your Google Analytics account. Search there for the title Mailchimp showed when you ticked the box: the email title plus the send date.