trust-dns-resolver looking up MX records in Rust

main.rs

use trust_dns_resolver::config::*;
use trust_dns_resolver::Resolver;

// Note you should add the crate to your Cargo.toml file
// trust-dns-resolver = "0.20.1"

fn main() {
    // Construct a new Resolver with default configuration options
    let resolver = Resolver::new(ResolverConfig::default(), ResolverOpts::default()).unwrap();

    // Lookup the IP addresses associated with a name.
    // The final dot forces this to be an FQDN, otherwise the search rules as specified
    //  in `ResolverOpts` will take effect. FQDN's are generally cheaper queries.
    let mx_response = resolver.mx_lookup("gmail.com.");

    // There can be many addresses associated with the name,
    //  this can return IPv4 and/or IPv6 addresses

    match mx_response {
        Err(_) => println!("No Records"),
        Ok(mx_response) => {
            let records = mx_response.iter();
            for record in records {
                println!("{} {}", record.preference(), record.exchange());
                let lookup_response = resolver.lookup_ip(record.exchange().to_string().as_str());
                match lookup_response {
                    Err(_) => println!("This exchange host has no address."),
                    Ok(lookup_response) => {
                        let ip_addrs = lookup_response.iter();
                        for ip_addr in ip_addrs {
                            if ip_addr.is_ipv4() {
                                println!("   ip4: {}", ip_addr)
                            } else {
                                println!("   ip6: {}", ip_addr)
                            }
                        }
                    }
                }
            }
        }
    }
}