From <URL:http://cr.yp.to/distributors.html>:

2022.11.15: I hereby place the serialmail package (in particular,
serialmail-0.75.tar.gz, with SHA-256 checksum
1825c911087f28692c3441d4f95747201c520a22575ab3e6132b5c14097038f3) into
the public domain. The package is no longer copyrighted.

Bump PKGREVISION for license change.

mail/serialmail/Makefile

@@ -1,15 +1,15 @@
-# $NetBSD: Makefile,v 1.14 2020/11/19 08:11:18 schmonz Exp $
+# $NetBSD: Makefile,v 1.15 2022/11/15 18:57:18 schmonz Exp $
 #
 
 DISTNAME=		serialmail-0.75
-PKGREVISION=		2
+PKGREVISION=		3
 CATEGORIES=		mail
 MASTER_SITES=		http://cr.yp.to/software/
 
 MAINTAINER=		schmonz@NetBSD.org
 HOMEPAGE=		https://cr.yp.to/serialmail.html
 COMMENT=		Tools for passing mail across serial links
-LICENSE=		djb-nonlicense
+LICENSE=		public-domain
 
 DEPENDS+=		qmail>=1.03nb7:../../mail/qmail