Opinions from people, evident in surveys and microblogging, for instance, may have bias or low user participation due to legitimate concerns about privacy and anonymity. To provide sender (the participant) anonymity, the identity of the message sender must be hidden from the message recipient (the opinion collector) and the contents of the actual message hidden from any intermediate actors (such as, routers) that may be responsible for relaying the message. We propose a novel one-way message routing scheme based on probabilistic forwarding that guarantees message privacy and sender anonymity through cryptographic means; utilising an additively homomorphic public-key cryptosystem along with a symmetric cipher. Our scheme involves intermediate relays and can work with either a centralised or a decentralised registry that helps with connecting the relays to each other. In addition to theoretical analysis, we demonstrate a real-world prototype built with HTML5 technologies and deployed on a public cloud environment. The prototype allows anonymous messaging over HTTP(S), and has been run inside HTML5 browsers on mobile application environments with no configurations at the network level. While we leave constructing the reverse path as future work, the proposal contained in this paper complete and has practical applications in anonymous surveys and microblogging.