Some singles web sites will collect random emails (or pay for them) and send unsolicited emails.
Totally understandable. Yeah those dating sites don't really care. I've posted items for sale on craigslist and will sometimes get unsolicited email from "women". It caused a similar problem in my household until I explained what happened.
I think it's important to talk to our partners about stuff like this first before getting upset. Sometimes it's just a simple misunderstanding.