lib/PublicInbox/IMAP.pm  | 15 ++++++---------
 lib/PublicInbox/IMAPD.pm |  2 +-
 t/imapd.t                |  2 +-
 xt/imapd-mbsync-oimap.t  |  2 +-
 xt/imapd-validate.t      |  2 +-

diff --git a/lib/PublicInbox/IMAP.pm b/lib/PublicInbox/IMAP.pm
index 6f64dff99585b738a75a2f076efed6a001a8daa7..5865822f0c3f12183d0390247e2ae590ee1c635b 100644
--- a/lib/PublicInbox/IMAP.pm
+++ b/lib/PublicInbox/IMAP.pm
@@ -197,14 +197,10 @@ 	my ($imapd, $ibx, $max) = @_;
 	my $mailboxes = $imapd->{mailboxes};
 	my $mb_top = $ibx->{newsgroup};
 	my @created;
-	my $uid_min = UID_BLOCK * int($max/UID_BLOCK) + 1;
-	my $uid_end = $uid_min + UID_BLOCK - 1;
-	while ($uid_min > 0) {
-		my $sub_mailbox = "$mb_top.$uid_min-$uid_end";
+	for (my $i = int($max/UID_BLOCK); $i >= 0; --$i) {
+		my $sub_mailbox = "$mb_top.$i";
 		last if exists $mailboxes->{$sub_mailbox};
 		$mailboxes->{$sub_mailbox} = $ibx;
-		$uid_end -= UID_BLOCK;
-		$uid_min -= UID_BLOCK;
 		push @created, $sub_mailbox;
 	}
 	return unless @created;
@@ -216,9 +212,9 @@ sub cmd_examine ($$$) {
 	my ($self, $tag, $mailbox) = @_;
 	my ($ibx, $mm, $max);
 
-	if ($mailbox =~ /\A(.+)\.([0-9]+)-([0-9]+)\z/) {
-		# old mail: inbox.comp.foo.$uid_min-$uid_end
-		my ($mb_top, $uid_min, $uid_end) = ($1, $2 + 0, $3 + 0);
+	if ($mailbox =~ /\A(.+)\.([0-9]+)\z/) {
+		# old mail: inbox.comp.foo.$uid_block_idx
+		my ($mb_top, $uid_min) = ($1, $2 * UID_BLOCK + 1);
 
 		$ibx = $self->{imapd}->{mailboxes}->{lc $mailbox} or
 			return "$tag NO Mailbox doesn't exist: $mailbox\r\n";
@@ -227,6 +223,7 @@ 		$mm = $ibx->mm;
 		$max = $mm->max // 0;
 		$self->{uid_min} = $uid_min;
 		ensure_ranges_exist($self->{imapd}, $ibx, $max);
+		my $uid_end = $uid_min + UID_BLOCK - 1;
 		$max = $uid_end if $max > $uid_end;
 	} else { # check for dummy inboxes
 		$ibx = $self->{imapd}->{mailboxes}->{lc $mailbox} or
diff --git a/lib/PublicInbox/IMAPD.pm b/lib/PublicInbox/IMAPD.pm
index 6488dc0f3bcbedbdd49fbcd6d2c9580e6f56e533..261d756042fbf7ee2856e486d11e28c46b3202e4 100644
--- a/lib/PublicInbox/IMAPD.pm
+++ b/lib/PublicInbox/IMAPD.pm
@@ -31,7 +31,7 @@ 		warn 'multiple newsgroups not supported: '.
 			join(', ', @$ngname). "\n";
 		return;
 	} elsif ($ngname =~ m![^a-z0-9/_\.\-\~\@\+\=:]! ||
-		 $ngname =~ /\.[0-9]+-[0-9]+\z/) {
+		 $ngname =~ /\.[0-9]+\z/) {
 		warn "mailbox name invalid: newsgroup=`$ngname'\n";
 		return;
 	}
diff --git a/t/imapd.t b/t/imapd.t
index 5d9a7d1181c78e907d6b46ffe787893b098e90bb..45ee401a1e0cfa598d10c07dde11da7a4b50c8f5 100644
--- a/t/imapd.t
+++ b/t/imapd.t
@@ -17,7 +17,7 @@ 	$imap_client = 'PublicInbox::IMAPClient';
 }
 
 require_ok 'PublicInbox::IMAP';
-my $first_range = '1-'.PublicInbox::IMAP::UID_BLOCK();
+my $first_range = '0';
 
 my $level = '-Lbasic';
 SKIP: {
diff --git a/xt/imapd-mbsync-oimap.t b/xt/imapd-mbsync-oimap.t
index b2cb8737f82264bcd2d8e30a68f465c605236850..fdaa22aa9efb868b1b4da4206cc4ef525f81da37 100644
--- a/xt/imapd-mbsync-oimap.t
+++ b/xt/imapd-mbsync-oimap.t
@@ -14,7 +14,7 @@ plan skip_all => "bad characters in $inboxdir" if $inboxdir =~ m![^\w\.\-/]!;
 my ($tmpdir, $for_destroy) = tmpdir();
 my $cfg = "$tmpdir/cfg";
 my $newsgroup = 'inbox.test';
-my $mailbox = "$newsgroup.1-50000";
+my $mailbox = "$newsgroup.0";
 {
 	open my $fh, '>', $cfg or BAIL_OUT "open: $!";
 	print $fh <<EOF or BAIL_OUT "print: $!";
diff --git a/xt/imapd-validate.t b/xt/imapd-validate.t
index b7b66d0583f49869ca94785e072505f02fb9050b..aeeb43b9b40f2de330286349830929a8154d30e2 100644
--- a/xt/imapd-validate.t
+++ b/xt/imapd-validate.t
@@ -39,7 +39,7 @@ 	%IMAPS_OPT = (%OPT, Port => 993) if $OPT{Port} == 143;
 } else {
 	require_mods(qw(DBD::SQLite));
 	$make_local_server->();
-	$mailbox = "$newsgroup.1-50000";
+	$mailbox = "$newsgroup.0";
 }
 
 my %opts = (imap => \%OPT, 'imap+compress' => { %OPT, Compress => 1 });