diff --git a/smtprelay.ini b/smtprelay.ini
index e6ed867..72942e4 100644
--- a/smtprelay.ini
+++ b/smtprelay.ini
@@ -14,6 +14,8 @@
 ;log_level = info
 
 ; path to alias file
+; alias file format (separated by space):
+; fake@email.tld real@email.tld
 ;aliases_file = aliases.txt
 
 ; Hostname for this SMTP server