Gmail is somewhat a special case because email services are kinda forced to accept inbound Gmail, even though it's quite a large source of scams and phishing attempts today. But for others, they'll still readily get blacklisted for a little while here and there.
I was thinking about spam as I read the post too, since this is a problem I get to deal with almost daily. Marketo has a terrible signal-to-noise ratio and it can often end up blackholed on my network with nary a user noticing. Sendgrid is my next least-favorite email-as-a-service, and in fact I happened to have this article open in one tab and in another tab I had this morning's automated reports from some of my spam software showing that a pile of inbound messages from Sendgrid had tried to land at a list of nonexistent mailboxes -- someone was rolling through "andy@", "barbara@", "vijay@", "kenneth@", etc.
I have had very little trouble with Mailgun in this regard, so far, but that may only be because the spammers haven't fully adopted them yet.
As a sysadmin on the receiving side, I really loathe these services, they make my job significantly harder and more time consuming than it used to be.