Curious, do you mean in business to business?

Otherwise I don't think you can argue any legitimate interest.

Yes, I mean cold sales emails – marketers reaching out to CEOs or other decision makers, selling them staff augmentation services, growth hacking, marketing support, lead generation, design services, etc. They'd claim legitimate interest by "personalizing" the email and claiming that it is relevant for you in a business sense. (Anyway, I don't think that these are fully compliant with GDPR either, because most often, they will have scraped your email address from somewhere, and do not provide a way to unsubscribe.)

Interesting, In my country that also seems to be illegal, e.g. cold calling can never be a valid reason(without consent).

https://www.ris.bka.gv.at/NormDokument.wxe?Abfrage=Bundesnor...

Edit:clarified never

Some countries provide some official places to complain about cold calls/emails, so at least it puts the sender at risk.

It boils down to a risk/reward trade-off, but I doubt that someone would as easily send thousands of spam mails, and also publicly boast about it