chore: AsRef is part of Rust's prelude

src/transport/sendmail/mod.rs

@@ -69,7 +69,6 @@ use crate::{Envelope, Transport};
 #[cfg(any(feature = "async-std1", feature = "tokio02"))]
 use async_trait::async_trait;
 use std::{
-    convert::AsRef,
     ffi::OsString,
     io::prelude::*,
     process::{Command, Stdio},

src/transport/smtp/commands.rs

@@ -9,10 +9,7 @@ use crate::{
     },
     Address,
 };
-use std::{
-    convert::AsRef,
-    fmt::{self, Display, Formatter},
-};
+use std::fmt::{self, Display, Formatter};
 
 /// EHLO command
 #[derive(PartialEq, Clone, Debug)]