Now even if we neglect the timeline, Rust only guarantees memory safety. If TB is deleting mails on the server too, then the corruption is happening over IMAP connections as well. Does that sound like a memory safety bug to you? Perhaps it is. But how do we eliminate the possibility of a logical bug that Rust won't protect you against, when nobody has any clue even now? And all that aside, if you're going to rewrite it in Rust, you might as well start a new project in Rust instead of porting an old design that may potentially contain a language-agnostic logical Heisenbug.
I'm not trying to be hostile here. I started using Rust in 2013 (I have 12 years of experience in a 10 year old language, and a bunch of repos that I can't compile anymore unless I compile the compiler from old commits somehow!). I wouldn't use C or C++ for any of these applications - I simply don't have enough competence to avoid the kind of bugs that Rust protects me from (despite being a hardware engineer with more knowledge about memory management than about type system theory). Despite all that, statements like this will only cause an unwanted backlash against Rust. Not that you're entirely wrong, but some people are so offended by such suggestions for reasons that are still under investigation, that they start a crusade against Rust [1].