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manifestor
Asked: 2021-02-26 03:41:39 +0800 CST

Postfix: How to keep an email in the mail queue for further investigation?

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Is there any way to keep an email in the Postfix mail queue for investigation/debugging purposes? I want delay the delivery and the email to be kept in the queue which let's me check it's contents. After I've done that I would flush the queue and let Postfix deliver it. How can I do this?

If it's not possible for a single email - would it be possible to queue all emails for a while?

debian email postfix email-server queue

1 Answers

  1. The HOLD feature should be sufficient for what you ask for, either use it on a message that is not yet delivered:

    postsuper -h QUEUEID

    Since you cannot know the queue ID in advance and might not be able to see it in the time between postfix queuing the mail and final delivery, I recommend defining the criteria for which messages to hold in advance.

    Most smtpd_*_restrictions allow providing a map that can automatically mark certain mails for holding. Sample:

    # in main.cf
smtpd_client_restrictions = [..]
    reject_unknown_reverse_client_hostname
    [..]
    check_reverse_client_hostname_access hash:/etc/postfix/badrdns permit

# in /etc/postfix/badrdns
.subdomains.example.com            HOLD one of these is not a spammer

    Release or drop mails from the queue after investigating.

    postqueue -p
# view a message from queue
postcat -qbhe QUEUEID | less

# deliver previously held
postsuper -H QUEUEID
# drop (DELETE!) a message
postsuoer -d QUEUEID

    Do not forget to remove the HOLD rule when done (or you accumulate a giant queue).

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