Why would PayPal send messages from another domain (“epl.paypal-communication”)?

Should the practice of sending messages from somecompany.com using anothercompany.com become established, it will be virtually impossible for us users telling if a website is legit or a scam.

Unfortunately, this practice is already established - and yes, it makes it very hard to tell legitimate communications from spam. Companies use partners and third parties to handle their email all the time. Why should a company (and in particular a company dealing with payments) send messages from another domain like “epl.paypal-communication”? This is because companies outsource non-core functions like marketing to third parties for economic reasons.

Why add countless trackers if you can already recognize users from logon? Trackers can provide a lot more psychographic information than logon can, and that information is valuable to marketing departments.