sendmail, 4th Edition

Role in Queue Management

A mail message can be temporarily undeliverable for a wide variety of reasons, such as when a remote machine is down or has a temporary disk problem. To ensure that such a message is eventually delivered, sendmail stores it in a queue directory until the message can be delivered successfully.

The QueueDirectory option in your configuration file tells sendmail where to find its queue directory:

O QueueDirectory=/var/spool/mqueue

The location of that directory must be a full pathname. Its exact location varies from vendor to vendor, but you can always find it by looking for the QueueDirectory option in your configuration file.

Beginning with V8.10, sendmail allows multiple queue directories to be used. Such a declaration can look like this:

O QueueDirectory=/var/spool/queues/q.*

Here, sendmail will use the subdirectories in /var/spool/queues that begin with the name q. for storage of messages. Such directories might be called, for example, q.00 and q.01.

If you have permission, take a look at a sendmail queue directory. It might be empty if no mail is waiting to be sent. If it is not empty, it will contain files such as these:

dfg17NVhbh002596 dfg1BHotav010793 qfg17NVhbh002596 qfg1BHotav010793

When a mail message is queued, it is split into two parts, each part being saved in a separate file. The header information is saved in a file whose name begins with the characters qf. The body of the mail message is saved in a file whose name begins with the characters df.