I'm looking for the definition of terms you use in traffic sources in Explorer: what's the difference between "email marketing", "webmails, and "portal sites"?

Piano Analytics natively distinguishes two source types:

• organic sources (by default, without tracking variable)

• marketing sources (tracking to implement)

Email marketing corresponds to e-mailing campaigns that generate traffic on the website. 

Webmails represent traffic from online messaging services, based on the JavaScript referrer.

As the main difference, we note that Email marketing is a marketing traffic source and Webmails is an organic traffic source. 

We define as portal sites any referrer listed as the URL for one of the sites of the organization that generated traffic on the analyzed site.

You can also find further information in this complete article about traffic sources: Traffic sources