diff --git a/mail-server/postfix.nix b/mail-server/postfix.nix
index d131fba..8164c3e 100644
--- a/mail-server/postfix.nix
+++ b/mail-server/postfix.nix
@@ -219,6 +219,7 @@ let
     bind_dn = ${cfg.ldap.bind.dn}
   '';
 
+  # Enforce a mapping between SMTP user and envelope sender address
   ldapSenderLoginMap = pkgs.writeText "ldap-sender-login-map.cf" ''
     ${commonLdapConfig}
     query_filter = ${cfg.ldap.postfix.filter}
@@ -233,6 +234,7 @@ let
     destination = ldapSenderLoginMapFile;
   };
 
+  # Check whether a recipient address exists, before accepting mail for it
   ldapVirtualMailboxMap = pkgs.writeText "ldap-virtual-mailbox-map.cf" ''
     ${commonLdapConfig}
     query_filter = ${cfg.ldap.postfix.filter}