git » spf » commit c7ba9eb

diff --git a/README.md b/README.md
index 8f8e28e..91cc3ae 100644
--- a/README.md
+++ b/README.md
@@ -14,12 +14,14 @@ It is used by the [chasquid](https://blitiri.com.ar/p/chasquid/) SMTP server.
 
 ## Example
 
-The API is quite simple: it has only one function to perform the SPF check,
-similar to the one suggested in the [RFC](https://tools.ietf.org/html/rfc7208).
+The API is quite simple: it has only one main function to perform the SPF
+check, similar to the one suggested in the
+[RFC](https://tools.ietf.org/html/rfc7208).
 
 ```go
-// Check if `ip` is authorized to send email for `domain`.
-result, err := spf.CheckHost(ip, domain)
+// Check if `sender` is authorized to send from the given `ip`. The `domain`
+// is used if the sender doesn't have one.
+result, err := spf.CheckHostWithSender(ip, domain, sender)
 if result == spf.Fail {
 	// Not authorized to use the domain.
 }
diff --git a/spf.go b/spf.go
index 8b8d940..c071b62 100644
--- a/spf.go
+++ b/spf.go
@@ -106,6 +106,9 @@ var (
 
 // CheckHost fetches SPF records for `domain`, parses them, and evaluates them
 // to determine if `ip` is permitted to send mail for it.
+// Because it doesn't receive enough information to handle macros well, its
+// usage is not recommended, but remains supported for backwards
+// compatibility.
 // Reference: https://tools.ietf.org/html/rfc7208#section-4
 func CheckHost(ip net.IP, domain string) (Result, error) {
 	trace("check host %q %q", ip, domain)
@@ -113,9 +116,9 @@ func CheckHost(ip net.IP, domain string) (Result, error) {
 	return r.Check(domain)
 }
 
-// CheckHostWithSender fetches SPF records for `domain`, parses them, and
-// evaluates them to determine if `ip` is permitted to send mail for it.
-// The sender is used in macro expansion.
+// CheckHostWithSender fetches SPF records for `sender`'s domain, parses them,
+// and evaluates them to determine if `ip` is permitted to send mail for it.
+// The `helo` domain is used if the sender has no domain part.
 // Reference: https://tools.ietf.org/html/rfc7208#section-4
 func CheckHostWithSender(ip net.IP, helo, sender string) (Result, error) {
 	_, domain := split(sender)