Sending unsolicited email to consumers is, indeed, spam. B2B is different.
EDIT: CANSPAM (US) is a bit ambiguous on this point. (Helpful blog post: http://customer.io/blog/Send-email-without-unsubscribe-link-...) CASL, its Canadian equivalent (I'm Canadian) is very clear on this point, though--unsolicited B2B to a publicly posted email address is a-ok, as long as it's not automated.
"Just to be clear, you’re not allowed to use Customer.io to send cold emails.."
Guess why :)
Edit: They are a business and have a "contact us" email on their website. Should I really not email them just because im not a customer, but a possible partner?
Another way of phrasing your mother's advice: "What if everybody did X?"
On the other hand, spamming or otherwise misusing email to deliver your unsolicited "message" at everyone else's expense is a classic instance of the Tragedy of the Commons. There is no incentive for any individual actor to do the right thing. Kant's categorical imperative is one of several reasonable ways to think about it.
I think the same for the email. If,everybody who can make a legitimate business proposal email them, no problem. And I apply the same ethics when I had my own company with a public email on my website (now im an employee and emails dont get to me)
Only if it is sent in bulk.
Unsolicited commercial email is spam, regardless of whether it is B2B, and regardless of whether it is sent to "public addresses".
Depends in which country you are in but in most EU countries, that is still spam and hence subject to legal action.
Edit: why the downvote? Care to explain your point?
I only use plain text emails. I don't even use email tracking so that hidden pixel doesn't trigger any annoying warning on the email client that ruins the experience.