kiwifidget:

 

Would I have got that email by chance, or do bad people know the email address associated with my OneDrive account?

 

They could have guessed it & got lucky (they do that)

or they could have got valid email adresses from:
some companies websites have company email adress (& user names) in there, these are harvested . They guess who the company accountant is & send them fake invoices
giving your email adress to any website or service that asks for it
giving your email adress to sftware companies
legit companies who have your email in their records getting hacked & email adresses harvested . Yahoo is a good example of that
other people who have you in their contact list getting hacked & contact list harvested by hackers

So, setup a junk email a/c with gmail. Thats the email adress you'll give out to those who dont really need it but insist otherwise