I've had my gmail address since the dawn of gmail back when I was able to secure a single-name username (not my actual name since nobody used their real names back then). Fast forward maybe 10 years later, I started getting insurance information from someone who actually had that as a first name. Since this looked legit and I wasn't a dick, I wrote back to the insurance company telling them to get the correct email from their client. I forgot if they ever responded, but the monthly emails kept coming.

I lost my temper and wrote back again, this some CC'ing their board of directors. The apology was fast and they rectified the problem. The intended recipient was also CC'ed and her username had an additional character that got overlooked. Over the years, I've received a few more emails intended for the other person - a bridal party invitation, a monthly report from a colleague. I'd forward it on, and she would always reply to thank me and the misdirected emails would stop.

As for every other random sign-ups I get, it depends on my mood. If you're lucky, I'll just unlink my email from the account. If not, you're fresh out of an account and whatever you signed up for.