Simple Address check via API So I have a wallet with thousands of addresses, I want to know how can I check the blockchain whether or not a transaction has been made to one(or another) of the addresses?
There are several API services that allow bulk address queries. 

For example smartbit's API takes up to 1,000 addresses with their v1/blockchain/addresses endpoint which will return details about each address sorting by the highest balance first. 

Example GET request:
https://api.smartbit.com.au/v1/blockchain/addresses/1DuMuchPBGNoi5b9JmpreZ2L5EpuMiJdyc,1N75aWck3TFPorTvSgdzLUttY8uddqTAFZ,161UqtBktXJMzcg2zxBGMiHgnVrtH78Amx,19eK34996XoXPgpranrUVSPLmkxzowt8ox

Link to API docs: https://www.smartbit.com.au/api