diff --git a/plugins/custom-login-mapping/README b/plugins/custom-login-mapping/README
index 39aafa739..e260527b2 100644
--- a/plugins/custom-login-mapping/README
+++ b/plugins/custom-login-mapping/README
@@ -1 +1,8 @@
-Plugin which allows you to set up custom username (login) by email address
\ No newline at end of file
+Plugin which allows you to set up custom username (login) by email address.
+
+Some mail servers use arbitrary usernames for logging in to the email service.
+This plugin replaces pre-@ email address with the predefined username for logging in.
+
+Usage:   <user email>:<username>
+Example: bob.jackson@mydomain.com:mydomain3
+By doing the above, users can log in with "bob.jackson@mydomain.com" instead of "mydomain3@mydomain.com"