lib/PublicInbox/Config.pm | 3 ++-
 t/mda.t                   | 2 +-

diff --git a/lib/PublicInbox/Config.pm b/lib/PublicInbox/Config.pm
index abc525dbbd5dca1cb6cb9e6c2adac0a4104d6f36..d57c361ad90cd8364629201021b485c7b715cb46 100644
--- a/lib/PublicInbox/Config.pm
+++ b/lib/PublicInbox/Config.pm
@@ -424,8 +424,9 @@ 		$self->{-by_addr}->{$lc_addr} = $ibx;
 		$self->{-no_obfuscate}->{$lc_addr} = 1;
 	}
 	if (my $listids = $ibx->{listid}) {
+		# RFC2919 section 6 stipulates "case insensitive equality"
 		foreach my $list_id (@$listids) {
-			$self->{-by_list_id}->{$list_id} = $ibx;
+			$self->{-by_list_id}->{lc($list_id)} = $ibx;
 		}
 	}
 	if (my $ng = $ibx->{newsgroup}) {
diff --git a/t/mda.t b/t/mda.t
index c7caf3e0cca455e3eb40088492b62f26f167ecc4..c5b35eec21cf40d30a5c0dc2abc829afab7b05d5 100644
--- a/t/mda.t
+++ b/t/mda.t
@@ -261,7 +261,7 @@ Subject: this message will be trained as spam
 Date: Thu, 01 Jan 1970 00:00:00 +0000
 
 EOF
-	xsys(qw(git config --file), $pi_config, "$cfgpfx.listid", $list_id);
+	xsys(qw(git config --file), $pi_config, "$cfgpfx.listid", uc $list_id);
 	$? == 0 or die "failed to set listid $?";
 	ok(run_script(['-mda'], undef, { 0 => \$in }),
 		'mda OK with List-Id match');