Messages queued for delivery are always stored in the same format, regardless of the type of channel in which they are queued. All messages are stored in subdirectories under the IMTA queue directory. There is usually one subdirectory per channel; its name is the same as the channel name. For example, messages queued for delivery in the Sun Message Store (sims-ms) channel are stored in the /var/opt/SUNWmail/imta/queue/sims-ms directory. Each file contains a single message.
Note - Some temporary files are stored in the top-level queue directory. The names of these temporary files usually begin with a dollar sign ($).
All of these directories are protected against access by non-privileged users. The first two characters of each file name are a representation of the number of times delivery has been attempted on the file. This information is encoded in "complemented base 36." For example, if no attempts have been made to deliver a message, the file name will begin with ZZ. The name will begin with ZY if one attempt has been made, ZA if 25 attempts have been made, Z0 if 35 attempts have been made, YZ if 36 attempts have been made, and so on.
The remainder of the file names are pseudo-random strings of hexadecimal characters that serve to make the file names unique. The file type (suffix) is always a pair of letters or digits, usually 00. Messages being held have .HELD as the file type; these messages are not eligible for delivery processing. Examine the .HELD files and correct the reason they could not be delivered. Then use imta queue-retry-delivery channel-name to deliver the .HELD messages.
The actual internal format of the message files is irrelevant. Those who wish to write their own IMTA channel programs, should access the messages via the documented IMTA API interface. However, it is sometimes useful for a system manager to examine messages in the queues, so it is helpful to note that messages are stored as ASCII text and message files may be typed on a terminal without adverse effects.