diff --git a/lib/licenses.nix b/lib/licenses.nix
index c370af346791..611e6ddb35b7 100644
--- a/lib/licenses.nix
+++ b/lib/licenses.nix
@@ -585,6 +585,11 @@ lib.mapAttrs (n: v: v // { shortName = n; }) rec {
     fullName = "Ruby License";
   };
 
+  sendmail = spdx {
+    spdxId = "Sendmail";
+    fullName = "Sendmail License";
+  };
+
   sgi-b-20 = spdx {
     spdxId = "SGI-B-2.0";
     fullName = "SGI Free Software License B v2.0";
diff --git a/pkgs/development/libraries/libmilter/default.nix b/pkgs/development/libraries/libmilter/default.nix
index bd0cd9fe9041..7e3c45634d9e 100644
--- a/pkgs/development/libraries/libmilter/default.nix
+++ b/pkgs/development/libraries/libmilter/default.nix
@@ -37,5 +37,6 @@ stdenv.mkDerivation rec {
     description = "Sendmail Milter mail filtering API library";
     platforms = platforms.unix;
     maintainers = with maintainers; [ fpletz ];
+    license = licenses.sendmail;
   };
 }