Hi @PMunar ,
You can get all utm_campaign data for a specific source indeed 
If you refer to this doc (which helped you get both urls above), you will see that you can use a parameter called d1 to dive a little bit deeper into the data that is returned to you.
If you run this call on your instance (add your own hapikey), you will see that you get the data for the email source only as well as a breakdown by campaign :
https://api.hubapi.com/analytics/v2/reports/sources/total?d1=email?hapikey=demo
Not all the sources will give you a breakdown by utm_campaign, to know which ones do, it’s actually quite simple : the API mimics what you can explore in the web analytics report.
Open Hubspot and go to Reports > Analytics Tools > Traffic Analytics.
The report should already be by source, you can then scroll down to get to the table data and click on any source to dive into a specific source data.
If the table shows utm_campaigns in the first column, that means the API will give you such a breakdown.
For example, here I clicked on “email marketing”.
If you want to know which values the d1 parameter can take, simply run this call :
https://api.hubapi.com/analytics/v2/reports/sources/total?hapikey=demo
In the JSON response, look for the breakdowns list and locate each breakdown value (example below).
"breakdowns": [
{
"breakdown": "organic",
"contactsPerPageview": 0.017413422030913714,
"returningVisits": 3334,
"rawViews": 5111,
"contactToCustomerRate": 0.38202247191011235,
"standardViews": 5111,
"customersPerPageview": 0.006652318528663667,
"sessionToContactRate": 0.02669466106778644,
"pageviewsPerSession": 1.5329934013197362,
"opportunities": 17,
"bounceRate": 0.35602879424115175,
"salesQualifiedLeads": 1,
"marketingQualifiedLeads": 1,
"visits": 3334,
"pageviewsMinusExits": 5111,
"leads": 3,
"leadsPerView": 5.869692819409117E-4,
"customers": 34,
"evangelists": 23,
"bounces": 1187,
"time": 450162,
"timePerSession": 135.02159568086384,
"contacts": 89,
"others": 10
}
]
Hope this helps !
If it does, please consider marking this answer as a solution 