Failed to understand "no longer could scientists read everything someone sent them; existing info...

What does "no longer could scientists read everything someone sent them; existing information filters became swamped" mean?

Why scientists could not read if someone sent them manuscripts? (I guess I've got the grammar wrongly). And what was the information filter? Was it like today's stupid China's internet filters? (Absolutely no. Again surely I got wrong grammar)

Context:

Henry Oldenburg created the first scientific journal in 1665 with a simple goal: apply an emerging communication technology — the printing press — to improve the dissemination of scholarly knowledge. The journal was a vast improvement over the letter-writing system that it eventually replaced. But it had a cost: no longer could scientists read everything someone sent them; existing information filters became swamped.

To solve this, peer and editorial review emerged as a filter, becoming increasingly standardized in the science boom after the Second World War. This peer-review system applies community evaluation of scholarly products by proxy: editorial boards, editors and peer reviewers are nominated to enact representative judgements on behalf of their communities.
MOre:
http://www.nature.com/nature/journal/v495/n7442/full/495437a.html