I've got Postfix 2.5.5 running on a Debian 5.0 server. Very small volume, no incoming mail, only sending out occasional notification emails sent from a web app and internal (system) emails like cron notifications. Web application sends mails using SMTP to localhost.
A few days ago, during a spike of web traffic, monitoring graphs for queue levels went up, and maildrop queue stays at 40 since then. Monitoring graphs number of files in /var/spool/postfix/*. After looking in, I see about 40 empty files in /var/spool/postfix/maildrop/.
When I use 'sendmail' after shutting down Postfix, a file appears in maildrop but it contains binary data; after starting Postfix, it disappears and mail is delivered. I can't find any information on empty files in the queue directory - is it expected? Harmful in any way? Or is making graphs look ugly its only function? Can I safely delete these files?