diff --git a/main.go b/main.go
index 6289bbc..cbd5993 100644
--- a/main.go
+++ b/main.go
@@ -20,6 +20,10 @@ func connectionChecker(peer smtpd.Peer) error {
 	// This can't panic because we only have TCP listeners
 	peerIP := peer.Addr.(*net.TCPAddr).IP
 
+	if len(allowedNets) == 0 {
+		// Special case: empty string means allow everything
+		return nil
+	}
 
 	for _, allowedNet := range allowedNets {
 		if allowedNet.Contains(peerIP) {
diff --git a/smtprelay.ini b/smtprelay.ini
index c1e90e8..91e1cc6 100644
--- a/smtprelay.ini
+++ b/smtprelay.ini
@@ -31,6 +31,7 @@
 ;local_forcetls = false
 
 ; Networks that are allowed to send mails to us
+; Defaults to localhost. If set to "", then any address is allowed.
 ;allowed_nets = 127.0.0.1/8 ::1/128
 
 ; Regular expression for valid FROM EMail addresses