I receive a ridiculous amount of other people's email - for serious things like email account reset, to banking info. When the Ashley Madison hack happened, my email address was there multiple times! Imagine if my then-partner had bothered to look, what a mess that would be.
I've called American Express a couple of times to report errant emails with account info ending up in my email. THEY didn't care that one of their customers had an issue, they thought it was a great time to have me fork over MY info "to check".
From time to time I have had messages relating to a government planning committee as one of the members got the domain of someone's departmental email account wrong and the messages come instead to the domain I administer.
In another instance I was getting emails about an account someone created with American Express using my email address. I sent multiple emails to their customer support to get them to stop sending financial information to the wrong person with no results. In this I also found it difficult to even figure out what agency to report them to for failing to take action when notified. Eventually I took the time to call them. It took around 20 minutes (not counting time on hold) of talking to multiple people to get them to remove the email address from the account. This included them asking me several times for my social security number - which I flatly refused to provide since I had zero business relationship with them. This refusal actually seemed to confuse them.
Many of the people I know who have very common gmail addresses have set up canned replies to let senders know they've reached the wrong person.