lib/PublicInbox/Unsubscribe.pm | 2 +-

diff --git a/lib/PublicInbox/Unsubscribe.pm b/lib/PublicInbox/Unsubscribe.pm
index 4ccdb7e0e33b38f8308650a4119a68cbc82bfe8a..97ff97f66eda6729ae42075c28b0e8174e9ed597 100644
--- a/lib/PublicInbox/Unsubscribe.pm
+++ b/lib/PublicInbox/Unsubscribe.pm
@@ -77,7 +77,7 @@ 		return r($self, 400, 'Bad request',
 			'Missing mailing list name in path component');
 	}
 	my $user = eval { $self->{cipher}->decrypt(decode_base64url($u)) };
-	if (!defined $user || $user eq '') {
+	if (!defined $user || index($user, '@') <= 1) {
 		my $err = quotemeta($@);
 		my $errors = $env->{'psgi.errors'};
 		$errors->print("error decrypting: $u\n");