The simple answer is no. Email is not a utm_source. It's a medium.
In Google Analytics a utm_source identifies the source, or origin, of where the traffic has come from.
An origin such as Facebook, Twitter, a referring website or your email newsletter.
But not email itself.
Email is the collective term for a type of platform just like social or organic search. This makes it a medium (utm_medium).
The simplest way to explain what I mean is by seeing concrete examples. Then understanding how Google Analytics uses utm tracking to provide campaign reports.
A concrete example of correct UTM tagging for email marketing
I run a website called the Worldbuilding School. At the time of writing it has over 2,500 email subscribers.
When subscribing to the email newsletter a subscriber is added to a list called “Worldbuilding School Newsletter”.
My email platform also has a list for customers and email accounts that have signed up for the membership area.
A subscribers email account may exist across all lists or it may exist in only one or two. For the purpose of this example it doesn’t matter.
At the point of subscribing to my list an email account will receive my welcome email. The utm parameters for a link in this email might look something like this:
Utm_campaign = welcome
Utm_medium = email
Utm_source = wbschool-newsletter
I would then use utm_content to identify individual links inside the email.
See how ‘email’ is recorded as the medium and the name of the list is recorded as the source. That is how it should be.