Read the contents of a message in the Postfix queue

If mailq is provided by Postfix, use postcat -q QUEUE_ID to inspect a queued message. mailq lists the queue; it does not display the full message content.

mailq
postcat -q A705238B4C
postcat -bh -q A705238B4C
postcat -h -q A705238B4C
postcat -b -q A705238B4C

The first postcat command shows envelope information and message content. -bh selects headers and body without the envelope; -h selects headers and -b selects the body. Reading queue files requires suitable permissions, so an administrator may need sudo.

Copy the ID without its status marker

The first column in a traditional queue listing can look like A705238B4C*. The suffix is not part of the ID:

Use the exact ID without the marker. Do not assume every ID is a short hexadecimal string: Postfix also supports long queue IDs.

Inspect selected headers across the queue

Postfix 3.1 or later supports structured queue output. With jq installed:

set -o pipefail
postqueue -j | jq -r '.queue_id' | while IFS= read -r id; do
  printf '\n=== %s\n' "$id"
  sudo postcat -h -q "$id" | grep -E '^(From|To|Subject|Date):'
done

Sample a few messages before inspecting a large queue. Headers can contain personal or sensitive information. The filter shows only the first line of matching headers; it does not unfold continuation lines or decode MIME-encoded subjects. Use a mail parser when you need the complete interpreted values.

The queue can change during enumeration. An ID may disappear between listing and reading, and the listing itself is not a consistent snapshot. A missing queue file can simply mean delivery finished.

Let Postfix locate the files

postconf queue_directory

The directory is often /var/spool/postfix. incoming contains newly queued mail, active contains messages selected for delivery, deferred contains delayed mail, and hold contains held messages. bounce stores per-message delivery-status information; it is not simply a mailbox of readable bounce emails. Queue storage may use hashed subdirectories, so use postcat -q rather than guessing a pathname.

Separate inspection from queue management

For delayed mail, inspect mailq, postqueue -j, and the logs for the recipient's delay reason. Original message headers do not necessarily explain a later delivery failure. Correlate the queue ID with DNS, routing, authentication, or remote-policy errors.

postqueue -f
sudo postsuper -h A705238B4C
sudo postsuper -H A705238B4C
sudo postsuper -d A705238B4C

These commands respectively request a queue flush, hold, release, and delete a message. They change state; deletion is permanent, and repeated full-queue flushes can worsen performance. If spam is accumulating, identify the submitting account or application before deleting the backlog. A forged From header alone does not identify the actual source.

References

• Postcat options
• Postqueue output and queue IDs

Related reading

• HEAD^ and HEAD~ in Git
• Check whether a server returns gzip-compressed content (Chinese)