Index: dovecot-2.2.13/src/pop3/pop3-client.c
===================================================================
--- dovecot-2.2.13/src/pop3/pop3-client.c
+++ dovecot-2.2.13/src/pop3/pop3-client.c	2015-11-17 19:12:46.817117794 +0100
@@ -194,6 +194,9 @@
 			client->last_seen_pop3_msn = msgnum + 1;
 		client->total_size += size;
 
+		if (client->highest_seq < mail->seq)
+			client->highest_seq = mail->seq;
+
 		array_append(&message_sizes, &size, 1);
 		msgnum++;
 	}
Index: dovecot-2.2.13/src/pop3/pop3-client.h
===================================================================
--- dovecot-2.2.13/src/pop3/pop3-client.h
+++ dovecot-2.2.13/src/pop3/pop3-client.h	2015-11-17 19:16:15.267610508 +0100
@@ -68,6 +68,7 @@
 
 	/* All sequences currently visible in the mailbox. */
 	ARRAY_TYPE(seq_range) all_seqs;
+	uint32_t highest_seq;
 
 	/* [msgnum] contains mail seq. anything after it has seq = msgnum+1 */
 	uint32_t *msgnum_to_seq_map;
Index: dovecot-2.2.13/src/pop3/pop3-commands.c
===================================================================
--- dovecot-2.2.13/src/pop3/pop3-commands.c
+++ dovecot-2.2.13/src/pop3/pop3-commands.c	2015-11-17 19:19:22.918645918 +0100
@@ -794,7 +794,7 @@
 	client->uidl_pool = pool_alloconly_create("message uidls", 1024);
 
 	/* first read all the UIDLs into a temporary [seq] array */
-	seq_uidls = i_new(const char *, client->messages_count);
+	seq_uidls = i_new(const char *, client->highest_seq);
 	str = t_str_new(128);
 	while (mailbox_search_next(search_ctx, &mail)) {
 		str_truncate(str, 0);
@@ -809,6 +809,7 @@
 		if (client->set->pop3_save_uidl && !permanent_uidl)
 			mail_update_pop3_uidl(mail, uidl);
 
+		i_assert(mail->seq <= client->highest_seq);
 		seq_uidls[mail->seq-1] = uidl;
 		hash_table_insert(prev_uidls, uidl, POINTER_CAST(1));
 	}