If you use Rust and want to learn about the Lettre crate for sending email using SMTP, here's a simple demonstration that can help with Lettre SMTP diagnostics and troubleshooting.

Feedback welcome, especially how to make it even easier for newcomers to diagnose SMTP issues. This code is all hand coded, no AI.

There are three implementations: synchronous, asynchronous with tokio1 rustls tls, asynchronous with tokio1 native tls.

https://github.com/joelparkerhenderson/demo-rust-lettre-sync

https://github.com/joelparkerhenderson/demo-rust-lettre-async-tokio1-rustls-tls

https://github.com/joelparkerhenderson/demo-rust-lettre-async-tokio1-native-tls