Persistent and unsubscribable spam
Out of the blue, I started receiving very persistent and frequent emails from 'apidays London'. Sometimes they would literally send three emails a day, all of them fairly generic, none of them of any relevance to me.
My email address had clearly been placed onto their mailing list without my knowledge or consent.
As each new, unwanted, email arrived I used the 'unsubscribe' feature in their email footer. Over the course of a couple of weeks I must have 'unsubscribed' dozens of times. The same inane, halfwitted, and irrelevant emails carried on arriving multiple times a day.
I eventually reached out to their founders and directors (their email addresses are on the Meet the Team page on their website). It took three attempts to elicit a response in which they assured me that I would receive no further emails.
Two days later, the asinine emails started arriving in my inbox again. It took another five days of emailing their team - again - before they agreed to stop.
Each time I emailed their board and team members, I asked for clarification on where they had obtained my (private, personal) email address from, and why I was on their list in the first place. I have never even heard of 'apidays', let alone agreed to receive their marketing emails. This request for further information has been outright ignored each time. Make of that what you will on the source of their email list.
It is fair to say - then - that they are utterly useless at maintaining a mailing list, and seemingly even operate it illegally.
Worse still: as far as I can tell from their (very poor) website, they really aren't any sort of authority on APIs either; just another set of scam conferences run by people who might have once read half a blog article on the subject, and understood less than half of that.
You would learn more about APIs by putting a paper bag over your head and having a shower than you will at one of their events.