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jmba - junk mail buffering agent


jmba [-d QUEUEDIR] [-m MSGFILE] [-s SUBJECT] [-FbtTv] [-f NUM[,KB]]
jmba [-d QDIR] [-e EXPIRY] [-x CMD] -q [-- COMMAND...]
jmba -S
jmba -[p|h|l|V]


jmba is a tool to queue email until the sender's email address has been verified, at which point the original email is delivered.

What this means is that when jmba receives an email, it puts that email into a queue instead of delivering it to you, and sends a message to the sender of the email. If the sender of the email responds correctly to jmba's message, the original email is unfrozen from the queue and delivered to you. If they do not, the original email eventually expires and you never see it.

jmba is designed to be used in conjunction with a spam filter such as qsf(1); when the spam filter says it thinks an email is spam, it can be passed to jmba, which can then verify whether a real person sent it or not.

This works on the assumption that senders of spam won't reply to the email address in the headers, but senders of real email will. The vast majority of spam is sent with forged envelope sender addresses so it always appears to have come from an invalid address.

For correct operation, four things are needed:

Deliver any email, without question, if the $1 parameter is JMBAPASSTHROUGH.
Pass any email with a subject line containing the reply email's SUBJECT (as defined by -s / --subject) to jmba, and do not deliver it.
Pass any other email you want filtered, e.g. email that qsf(1) or other spam filters suggest is spam, to jmba, and do not deliver it.
Regularly run jmba -q to deliver any queued email into your mailbox whose sender has verified their existence.

See the EXAMPLES section for examples of how this can be done.


The jmba options are listed below.

-d, --queue-dir DIR
Store queued messages in DIR, instead of the default of $HOME/.jmba/queue.
-e, --expiry-time DAYS
Expire queued messages after DAYS days, instead of the default of 28.
-m, --message-file FILE
Read the reply template from FILE instead of the default of $HOME/.jmba/template. See the FILES section for information on the contents of this file.
-D, --discard-dir DIR
Store discarded messages in DIR, instead of the default of $HOME/.jmba/discarded. See the FILES section for more information.
-L, --log-file FILE
Enable logging, and write logs to FILE instead of the default of $HOME/.jmba/log.
-x, --discard-command COMMAND
Each time a message is discarded, run COMMAND with the message on standard input. This can be useful for retraining spam filters; for instance the command could be qsf --mark-spam. Note that COMMAND should be quoted from the shell so it appears as one argument.
-s, --subject STRING
Use STRING as the subject line of each reply, instead of the default of "Email queued by JMBA". A message ID string will be added to the end of this string.
-t, --no-to-self
Discard any email whose "From:" and "To:" addresses are the same, instead of generating replies. This is enabled by default.
-T, --to-self, --allow-to-self
Allow email whose "From:" and "To:" addresses are the same to generate replies.
-v, --verbose
Log information about what jmba is doing to the log file ($HOME/.jmba/log by default).
-f, --flood-check NUM[,KB]
Before queueing a message, check the last KB kilobytes of the log file (default 50) for messages from the same sender address which were queued but which have not yet bounced or been unlocked. If there are more than NUM of them (default 20), discard the message instead of queueing it. This helps prevent flooding caused by brain-dead autoresponders, and is enabled by default.
-F, --no-flood-check
Switch off flood checking.
-b, --bounce
Assume that the email on standard input is a bounce message. The email is not queued, and if a valid queue ID is found within the email, the queued email it refers to is deleted. This allows queued messages from invalid senders to be removed from the queue early.
-q, --queue -- COMMAND
For every message in the queue that has been flagged as OK, run COMMAND with the message on standard input and delete the message if the command exited successfully. All subsequent command line items are taken as part of the command, eg jmba -q -- procmail -a JMBAPASSTHROUGH -d $LOGNAME. The default command, if none is specified, is procmail -a JMBAPASSTHROUGH -d $LOGNAME.
-S, --decode-subject
Read an email on standard input, find the first subject line, decode it if it is encoded, and output it on standard output.
-p, --procmail
Print an example procmail(1) recipe on standard output and exit successfully.
-h, --help
Print a usage message on standard output and exit successfully.
-l, --license
Print details of the program's license on standard output and exit successfully.
-V, --version
Print version information on standard output and exit successfully.


These files and directories are created automatically if they do not exist and you have not specified an alternative.

The default queue directory. This is where queued messages are stored. Make sure there is enough space in this directory to store plenty of queued mail.
The default reply template. The reply template is the message that gets sent in reply to any incoming email, and must contain the string {MESSAGEKEY} (all capitals, surrounded by {} curly braces) somewhere. The {MESSAGEKEY} text is replaced by a special string which identifies the original message. The recipient must reply back, with the subject line unchanged and the message body containing this string, for their original message to be unfrozen.

The template can also contain {MESSAGECODE}, which is replaced by just the 32-character hex code on its own, {USER}, which is replaced by the username that jmba is running under, {SENDER}, which is replaced by the email address of the original sender, {RECIPIENT}, which is replaced by the email address the message was sent to (i.e. your email address) if it appeared in the To: header - or "<unknown>" if it didn't - and {ORIGINAL}, which is replaced by an excerpt (around 9 lines) of the message jmba is replying to.

If this directory exists (it is not created by default), then any messages that are thrown out of the queue due to either a bounce message or a reply timeout will be moved here instead of deleted. This can be useful if you want to keep a copy of old spam to retrain spam filters with. Note: this directory must be on the same filesystem as the queue directory, otherwise it will not work.
The default log file, written to if the -v (verbose) option is given.


The following can be added to your .procmailrc file, after any special filtering you already do for mailing lists and such:

 # Example procmail recipe
 # Put this AFTER rules for mailing lists,
 # so that we don't trip up on them!
 # First, we'll set up some variables.
 JMBASUBJECT="Email queued by JMBA"
 SUBJECT=`jmba -S`
 # Step 1:
 # Filter messages only if the pass-through flag
 # is not set and the message is small.
 * ! > 500000
    # Step 2:
    # Discard any looping mail.
    * $ ^X-Loop: $JMBAMAINEMAIL
    # Step 3:
    # Deal with any bounces.
       :0 Bw
       * $ SUBJECT ?? .*$JMBASUBJECT
       | jmba -v -b
       :0 Bw
       * $ ^X-Loop: $JMBAMAINEMAIL
       | jmba -v -b
    # Step 4:
    # Pass any sender's replies straight to the program.
    :0 w
    * ! ^FROM_DAEMON
    | jmba -v -s "$JMBASUBJECT"
    # Step 5:
    # Check whether message is spam.
    :0 wf
    | qsf -ra
    # Step 6:
    # Drop potential spam into the
    # queue, and send the reply email.
    * ! ^FROM_DAEMON
    * ! ^X-Spam: NO
       # Generate the reply.
       :0 wf
       | jmba -t -v -s "$JMBASUBJECT"
       :0 Ha
          # Discard unaddressed responses.
          * ! ^To
          # Add our loop catching header.
          :0 wf
          | formail -A "X-Loop: $JMBAMAINEMAIL"
          # Add our From: address.
          :0 wfa
          | formail -I "From: $JMBAMAINEMAIL"
          # Send the reply.
          :0 wa
 # Step 7:
 # Teach the spam filter that passed-through
 # messages are not spam.
 :0 wc
 | qsf -Ma
 # End of example.
 # Don't forget to add "0 * * * * jmba -v -q"
 # to your crontab!

Note that the above recipe can be generated by doing jmba -p > SOME-FILE.

Then, add the following to your crontab(5) using the crontab -e command, to deliver any queued messages that have been verified once an hour:

 0 * * * * jmba -v -q

If you do not want to use qsf(1) as your spam filter, replace qsf -ra in the example procmail recipe above with a command that adds a header saying whether the email is spam, replace qsf -Ma with a command that trains the spam filter to accept the given email on standard input as non-spam, and replace the * ! ^X-Spam: NO line in step 6 with a rule that uses your spam filter's inserted header to cause step 6 to be skipped if the email is not spam.

For more on procmail(1) recipes, see the procmailrc(5) and procmailex(5) manual pages. For more on command scheduling, see the crontab(1) and crontab(5) manual pages.


If the full path of procmail is not found at compile time, then it will be called without a path. This means that users who are not supposed to have shell accounts, but who have write access to a directory in the default $PATH (such as ~/bin on some systems), could upload a fake procmail and gain shell access.

Also, some systems do not set $PATH when running cron jobs.

It is therefore advisable to supply the full path when specifying a procmail command with the -q -- COMMAND option. The default command contains the full path if no warning was generated at compile time.

This same problem exists with formail, which is called by jmba, but this can only be overcome if the full path to formail is correctly determined at compile time.


The project maintainer is:

Andrew Wood

Credit is also due to:

Ondrej Suchy
(provided Czech translation and code suggestions)
Nick Rosier
(suggested logging)

Project home page:


If you find any bugs, please contact the author, either by email or by using the contact form on the web site.


procmail(1), crontab(1), procmailrc(5), procmailex(5), crontab(5), qsf(1)


This is free software, distributed under the ARTISTIC license.

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