Being careful with your email on the net....

[SuperFlyer]

Check if your email was found in breached/compromised sites:

https://haveibeenpwned.com/

(One of my emails were, and it seems pretty accurate...)

Not much you can do about it now, but it does give a fair idea.

[Freddie]

maybe this site mines email addresses?
that's the first thing that popped into my head.

[SuperFlyer]

maybe this site mines email addresses?
that's the first thing that popped into my head.

that's the logic I would use.
 however from the person it was sent to me, it's not an option.

[Aaaron]

It's a well-known, accurate site.

My main email was breached in the old Adobe and the LinkedIn hacks.

[Randomex]

I just heard about this recently. Unless you're high-profile in some way, the main thing to worry about
isn't people accessing your email account but "credential stuffing" - people using programs to test known
email/password combinations against sites/apps where there's value in gaining access to accounts.
So, problems only usually happen if you use the same password for for your email and other things.

Because of this, I think using a single password pattern like dansdeals876/gmail876/facebook876 isn't
as bad as it might sound, seeing as no one's examining breached email/PW combinations individually
(unless, as mentioned, there's reason for specific interest in you).

Trivia: The site's Wikipedia page notes at the top that it is not the page for Hebrew Institute of Boro Park
(aka Yeshivas Etz Chaim), the first day school in Borough Park.