Rust By Example is very good for showing the ropes in a very practical way, that's how I got up and running with it.
Secondly is the O’Reilly book Programming Rust, which is probably closer to what you want, it explains the actual technical details of much of the language, and to me seems written for an audience that already knows programming. Lastly would be Rust for Rustaceans by No Starch Press, if you actually do want to pursue Rust further, as it discusses very, very in detail the systems of the language, and how they can be used to make something so powerful like Serde.
I've read this with concerning frequency, was SPF/DMARC/DKIM all in order? I also have to question if it was a matter of IP reputation, since shared hosting IP ranges are usually pretty thrashed.
I rent mailbox services (for a custom domain) from a local ISP and don't have problems with deliverability as such.