Need help with email UTMs

[Milena_Volkova]

Hi all. I inherited a Marketo instance where a lot of things were developed over the years by different people. I am now trying to make my UTMs work in email.

What we need to happen is: 

When someone clicks a link for webinar registration, record the following in custom fields (note: these custom fields are also used by the javascript that captures UTM parameters from a form fill): 

• Source - Last: UTM Source = mkto
• Source - Last: UTM Medium = email
• Source - Last: UTM Campaign = nurture

Here's what's happening: 

By default all email clicks get these values (notice the fields are different; are they out of the box?): 

utm_source: mkto

utm_medium: email

I don't know where to change these fields to the ones I need, i.e., where in Marketo I can specify the custom fields (Source - Last: UTM Source etc.) to be used for email clicks. 

In our email template, there is also a way to set a Global Variable for UTM Campaign (again, NOT the field we are using; likewise, I don't know how to change what field Marketo should use for it); also, there is only UTM Campaign field in the Global Variables, not utm_source or utm_medium (I don't need those fields, anyway, I need to use my custom fields like Source - Last: UTM Source etc.).

Alternatively, I can enter the full URL like www.company.com/asset_name/?utm_source=marketo&utm_medium=email&utm_campaign=nurture in the CTA button URL, but it's a lot easier to have the source and medium for all email clicks to be set automatically, and even if I enter that whole URL every time, it gets messed up. Marketo still wants to use the UTM Campaign field rather than the field I need (i.e., Source - Last: UTM Campaign). 

It looks like an external process (the javascript?) updates that field, but there is no reference to it in the UTM capture javascript. 

Sorry, this is so convoluted. Any help would be appreciated.