diff --git a/README.md b/README.md
index ea4cdc1..ce449ad 100644
--- a/README.md
+++ b/README.md
@@ -66,6 +66,8 @@ text.send('1119491234567', 'Bonjour!', 'intl', function(err) {
 
 Textbelt can be run as a standalone server with: `node server/app.js`.  Be sure to install dependencies first with `npm install`. This project also relies on redis. To install redis locally, please see the [redis documentation](http://redis.io/topics/quickstart). Before launching the app, ensure redis is running on port 6379 with `redis-server`.
 
+Textbelt also depends on a local installation of `mutt`, the email client (http://www.mutt.org/).  On Linux (Ubuntu), you can `sudo apt-get install mutt`.  On macs, you can `brew install mutt`.
+
 By default, the server listens on port 9090 and is configured to accept traffic from a reverse proxy or load balancer such as nginx.  To enable accurate IP rate limiting, the reverse proxy should be configured to set the `X-Real-IP` header.
 
 Don't forget to set `fromAddress` in `lib/text.js` to the email address you want to send from.