commit 7847bd6699c420695652cd446d540ead1d8be64c
from: Martijn van Duren <martijn@openbsd.org>
date: Tue Apr 05 10:55:17 2022 UTC

Domains are case insensitive.
Keep that in mind when comparing i- and d-tag

commit - 022782a1659fc7933b5f5dbdbe537234514778ee
commit + 7847bd6699c420695652cd446d540ead1d8be64c
blob - 8dfe64a3a999c61c092e1c44a4698c6cf6d49db7
blob + 88350035dd2a77139926a2d192b6fcd9596f9b24
--- main.c
+++ main.c
@@ -493,7 +493,7 @@ dkim_signature_parse(struct header *header)
 		}
 		i += ilen - dlen;
 		if ((i[-1] != '.' && i[-1] != '@') ||
-		    strncmp(i, sig->d, dlen) != 0) {
+		    strncasecmp(i, sig->d, dlen) != 0) {
 			dkim_signature_state(sig, DKIM_PERMERROR,
 			    "i tag not subdomain of d");
 			return;