Let's start with this scenario:
We have a mailbox (i.e. in yahoo), every message is sent by this account, marked as spam by Gmail spam filter. (because the address or sender IP is blacklisted, not because of content)
There is a server which is able to forward incoming messages to another address (email forwarding), for example, to a Gmail mailbox. And it is not blacklisted.
The question is: If we send a message, through the dirty mailbox to the server, and server forward it to a Gmail mailbox, will it marked as spam by spam filters?