A client with address A signs a raw transaction, and leaves it all ready to be sent, gives it to the server with address B, which later will send it with sendSignedTransaction(...).
What will be the values of:
msg.sender
tx.origin
EDIT: Notice this is NOT a duplicate of this other question, since in the other question the answers and the questions are oriented towards contract vs. non-contract addresses, whereas here both addresses A and B are not contracts, but in this case A signs and server with address B sends.