When I sign up somewhere, I often use

my.emailaddress+service@gmail.com

And then occasionally spam comes into my mailbox "hi person, you singed up for spam service" send to my.emailaddress+spotify@gmail.com

and well, now I know who sold it

also also, type your email into haveibeenpwnd.com to find if it's leaked somewhere

Doesn't matter how careful you are if the people close yo you with that information aren't.

'Why yes ofcourse you can access my address book in order for me to play candy crush.'

If you have signed up on dubious websites with questionable privacy policy, many of them legally sell this data to "data brokers" who then sell it to anyone willing to pay. This happens more than you'd think, for example in 2019 it was reported California DMV makes $50 million a year selling users information. https://www.caranddriver.com/features/a32035408/dmv-selling-driver-data/

One neat trick is to signup for services with an email like name+website@domain.com, that way if you ever get spam you'll know where you have been compromised.

A few months ago was the largest data breach possibly ever. Something like 300GB of personal information. Basically everyone in the US. They have everything on everyone and it's being passed all around on the dark web like skittles. The mainstream media didn't cover this for whatever reason.

Some companies just blatantly sell your data. Others get breached and you are part of the package that gets sold by the hackers.

The only "way around" is to use unique mail addresses for each signup/company so you can easily lock it and switch to another one when it gets known.

Just assume, that everything that you type in a form online (or in any other way send to a company/another person digitally), every email you send, everything that gets digitized about you, etc. will be public one day. Either because the other side of the transaction sold it or because they (or you) will be hacked eventually.

Btw: HaveIBeenPwned does not necessarily contain all breaches. I have several notifications of companies that got breached and leaked my data that are not listed in HIBP...

Someone who you've corresponded with over email had their address book compromised and it was used in a mass phishing email campaign. It's not necessarily targeted at you. I actually have experience of this happening. I had an email address that I used only to correspond to a single person. I never gave the email to anyone else and never signed up for anything. Well that person's email was compromised and I started getting spam/phishing emails shortly after that.

This is gonna sound silly but check here:

https://haveibeenpwned.com/

Might have some info if you’ve had creds leak or get exposed somewhere.

Nvm, just re-read your post and saw you already did. Leaving this up for the link for others. Sorry to bother!

employees of companies with whom you've registered that email id sell it for some quick cash on the side.

i can aver this confidently since i know someone from dominos pizza has leaked my email id. i have a convoluted gmail id which i use to register to all these services and -- because it's gmail -- i can set up random dots and a custom phrase behind a + to register specific variants to specific companies (e.g., abcxyz123@gmail vs. ab.c.xyz123+dominos@gmail).

all the spam and pseudo-phishing email is sent only to the variant which i've registered to dominos and not to a different variant (e.g., a.bcxyz123+bankname@gmail) registered to any other company.

the leaked email id doesn't contain a name and is too random for it to just be "guessed" by the spammers.

Have you given your email address to any other people you know? If so they probably put it into their contacts. They then use apps like whatsapp, insta, snap, etc which request access to their contacts. These companies then sell that information to ad companies. Tadaaa.

One possibility is that you have a fairly common username part and a similarly common domain like, say, gmail.

There's nothing stopping a spammer from taking existing addresses and word lists, then taking them apart and putting them together in different ways to make up completely new addresses to send spam to. It doesn't matter if 99% of the addresses they make up don't exist because they're only interested in the 1% of the 1% of successes who will fall for their scam. They don't even get the rejections because the From address is usually bogus too.

e.g. I bet whoever owns john dot smith at gmail gets a huge amount of spam whether he's in any databases or not.

It can happen in many ways. If you've ever used your mail for anything, then the address is out there.

Just the other day I got an email addressed to 50+ people with every email in the "to" field. Ironically the mail was about online security...

Obviously it's a breach on GDPR, but the damage is already done. If just one of the other recipients has been hacked or has forwarded to someone who is or has allowed some dodgy app to syncronize contracts, the scamners now has all the emails.

There's absolutely nothing I could have done to prevent it.

Probably a breach that's not on have I been pwned yet.

yahoo! mail offers throw away aliases you can delete if you get spam on one.