add keywords

README.md

@@ -524,7 +524,7 @@ See also [http://areweideyet.com/](http://areweideyet.com/) and [Rust and IDEs](
 
 ### Email
 
-[[email](https://crates.io/keywords/email)]
+[[email](https://crates.io/keywords/email), [imap](https://crates.io/keywords/imap), [smtp](https://crates.io/keywords/smtp)]
 
 * [gsquire/sendgrid-rs](https://github.com/gsquire/sendgrid-rs) — unofficial Rust library for SendGrid API [<img src="https://travis-ci.org/gsquire/sendgrid-rs.svg?branch=master">](https://travis-ci.org/gsquire/sendgrid-rs)
 * [lettre/lettre](https://github.com/lettre/lettre) — an SMTP-library for Rust [<img src="https://travis-ci.org/lettre/lettre.svg?branch=master">](https://travis-ci.org/lettre/lettre)