lib/PublicInbox/IMAPD.pm | 7 +++++++
 t/imap.t                 | 7 ++++++-
 t/imapd.t                | 2 +-

diff --git a/lib/PublicInbox/IMAPD.pm b/lib/PublicInbox/IMAPD.pm
index a3a2598661bbf97d09b0c5ddb550f5c9faeca506..966879d8ea59f76e8401468e09db7953bbc269c2 100644
--- a/lib/PublicInbox/IMAPD.pm
+++ b/lib/PublicInbox/IMAPD.pm
@@ -25,6 +25,13 @@ sub refresh_inboxlist ($) {
 	my ($self) = @_;
 	my @names = map { $_->{newsgroup} } @{delete $self->{grouplist}};
 	my %ns; # "\Noselect \HasChildren"
+
+	if (my @uc = grep(/[A-Z]/, @names)) {
+		warn "Uppercase not allowed for IMAP newsgroup(s):\n",
+			map { "\t$_\n" } @uc;
+		my %uc = map { $_ => 1 } @uc;
+		@names = grep { !$uc{$_} } @names;
+	}
 	for (@names) {
 		my $up = $_;
 		while ($up =~ s/\.[^\.]+\z//) {
diff --git a/t/imap.t b/t/imap.t
index 451b6596bf9f8d08df021a385d597fcb8eebb807..aa262a196329f49d79808c7b4c951a6fb5ecc81f 100644
--- a/t/imap.t
+++ b/t/imap.t
@@ -8,9 +8,14 @@ use PublicInbox::IMAP;
 use PublicInbox::IMAPD;
 
 { # make sure we get '%' globbing right
-	my @n = map { { newsgroup => $_ } } (qw(x.y.z x.z.y));
+	my @w;
+	local $SIG{__WARN__} = sub { push @w, @_ };
+	my @n = map { { newsgroup => $_ } } (qw(x.y.z x.z.y IGNORE.THIS));
 	my $self = { imapd => { grouplist => \@n } };
 	PublicInbox::IMAPD::refresh_inboxlist($self->{imapd});
+	is(scalar(@w), 1, 'got a warning for upper-case');
+	like($w[0], qr/IGNORE\.THIS/, 'warned about upper-case');
+
 	my $res = PublicInbox::IMAP::cmd_list($self, 'tag', 'x', '%');
 	is(scalar($$res =~ tr/\n/\n/), 2, 'only one result');
 	like($$res, qr/ x\r\ntag OK/, 'saw expected');
diff --git a/t/imapd.t b/t/imapd.t
index 2c4315dec30fb19b003a790944ebb2c7e0227a0d..a5324f78da0044b3c82113c46a2057ed7f2844e5 100644
--- a/t/imapd.t
+++ b/t/imapd.t
@@ -88,7 +88,7 @@ like($e, qr/\bNO\b/, 'got a NO on EXAMINE for non-existent');
 ok(!$mic->select('foo') && ($e = $@), 'EXAMINE non-existent');
 like($e, qr/\bNO\b/, 'got a NO on EXAMINE for non-existent');
 ok($mic->select('inbox.i1'), 'SELECT succeeds');
-ok($mic->examine('inbox.i1'), 'EXAMINE succeeds');
+ok($mic->examine('INBOX.i1'), 'EXAMINE succeeds');
 my @raw = $mic->status('inbox.i1', qw(Messages uidnext uidvalidity));
 is(scalar(@raw), 2, 'got status response');
 like($raw[0], qr/\A\*\x20STATUS\x20inbox\.i1\x20