formail - mail (re)formatter
formail [+skip] [-total] [-bczfrktedqBY] [-p prefix]
[-D maxlen idcache]
[-x headerfield] [-X headerfield]
[-a headerfield] [-A headerfield]
[-i headerfield] [-I headerfield]
[-u headerfield] [-U headerfield]
[-R oldfield newfield]
[-n [maxprocs ]] [-m minfields] [-s [command [arg ...]]]
formail is a filter that can be used to force mail into mailbox format,
perform `From ' escaping, generate auto-replying headers, do simple
header munging/extracting or split up a mailbox/digest/articles file.
The mail/mailbox/article contents will be expected on stdin.
If formail is supposed to determine the sender of the mail, but is
unable to find any, it will substitute `foo@bar'.
If formail is started without any command line options, it will force
any mail coming from stdin into mailbox format and will escape all
bogus `From ' lines with a `>'.
-v Formail will print its version number and exit.
-b Don't escape any bogus mailbox headers (i.e., lines starting with
Define a different quotation prefix. If unspecified it defaults
-Y Assume traditional Berkeley mailbox format, ignoring any Content-
-c Concatenate continued fields in the header. Might be convenient
when postprocessing mail with standard (line oriented) text
-z Ensure a whitespace exists between field name and content. Zap
fields which contain only a single whitespace character. Zap
leading and trailing whitespace on fields extracted with -x.
-f Force formail to simply pass along any non-mailbox format (i.e.,
don't generate a `From ' line as the first line).
-r Generate an auto-reply header. This will normally throw away all
the existing fields (except X-Loop:) in the original message,
fields you wish to preserve need to be named using the -i option.
If you use this option in conjunction with -k, you can prevent the
body from being `escaped' by also specifying -b.
-k When generating the auto-reply header or when extracting fields,
keep the body as well.
-t Trust the sender to have used a valid return address in his
header. This causes formail to select the header sender instead
of the envelope sender for the reply. This option should be used
when generating auto-reply headers from news articles or when the
sender of the message is expecting a reply.
-s The input will be split up into separate mail messages, and piped
into a program one by one (a new program is started for every
part). -s has to be the last option specified, the first argument
following it is expected to be the name of a program, any other
arguments will be passed along to it. If you omit the program,
then formail will simply concatenate the split mails on stdout
again. See FILENO.
Tell formail not to wait for every program to finish before
starting the next (causes splits to be processed in parallel).
Maxprocs optionally specifies an upper limit on the number of
concurrently running processes.
-e Do not require empty lines to be preceding the header of a new
message (i.e., the messages could start on every line).
-d Tell formail that the messages it is supposed to split need not be
in strict mailbox format (i.e., allows you to split
digests/articles or non-standard mailbox formats). This disables
recognition of the Content-Length: field.
Generate a log summary in the same style as procmail. This
includes the entire "From " line, the Subject: header field, the
folder, and the size of the message in bytes. The mailstat
command can be used to summarize logs in this format.
-B Makes formail assume that it is splitting up a BABYL rmail file.
Allows you to specify the number of consecutive headerfields
formail needs to find before it decides it found the start of a
new message, it defaults to 2.
-q Tells formail to (still detect but) be quiet about write errors,
duplicate messages and mismatched Content-Length: fields. This
option is on by default, to make it display the messages use -q-.
-D maxlen idcache
Formail will detect if the Message-ID of the current message has
already been seen using an idcache file of approximately maxlen
size. If not splitting, it will return success if a duplicate has
been found. If splitting, it will not output duplicate messages.
If used in conjunction with -r, formail will look at the mail
address of the envelope sender instead at the Message-ID.
Extract the contents of this headerfield from the header. Line
continuations will be left intact; if you want the value on a
single line then you'll also need the -c option.
Same as -x, but also preserves/includes the field name.
Append a custom headerfield onto the header; but only if a similar
field does not exist yet. If you specify either one of the field
names Message-ID: or Resent-Message-ID: with no field contents,
then formail will generate a unique message-ID for you.
Append a custom headerfield onto the header in any case.
Same as -A, except that any existing similar fields are renamed by
prepending an ``Old-'' prefix. If headerfield consists only of a
field-name, it will not be appended.
Same as -i, except that any existing similar fields are simply
removed. If headerfield consists only of a field-name, it
effectively deletes the field.
Make the first occurrence of this field unique, and thus delete
all subsequent occurrences of it.
Make the last occurrence of this field unique, and thus delete all
preceding occurrences of it.
-R oldfield newfield
Renames all occurrences of the fieldname oldfield into newfield.
Skip the first skip messages while splitting.
Output at most total messages while splitting.
When renaming, removing, or extracting fields, partial fieldnames may
be used to specify all fields that start with the specified value.
By default, when generating an auto-reply header procmail selects the
envelope sender from the input message. This is correct for vacation
messages and other automatic replies regarding the routing or delivery
of the original message. If the sender is expecting a reply or the
reply is being generated in response to the contents of the original
message then the -t option should be used.
RFC822, the original standard governing the format of Internet mail
messages, did not specify whether Resent header fields (those that
begin with `Resent-', such as `Resent-From:') should be considered when
generating a reply. Since then, the recommended usage of the Resent
headers has evolved to consider them as purely informational and not
for use when generating a reply. This has been codified in RFC2822,
the new Internet Message Format standard, which states in part:
Resent fields are used to identify a message as having been
reintroduced into the transport system by a user. The purpose
of using resent fields is to have the message appear to the
final recipient as if it were sent directly by the original
sender, with all of the original fields remaining the
same....They MUST NOT be used in the normal processing of
replies or other such automatic actions on messages.
While formail now ignores Resent headers when generating header
replies, versions of formail prior to 3.14 gave such headers a high
precedence. If the old behavior is needed for established applications
it can be specified by calling formail with the option `-a Resent-' in
addition to the -r and -t options. This usage is deprecated and should
not be used in new applications.
While splitting, formail assigns the message number currently
being output to this variable. By presetting FILENO, you can
change the initial message number being used and the width of the
zero-padded output. If FILENO is unset it will default to 000.
If FILENO is non-empty and does not contain a number, FILENO
generation is disabled.
To split up a digest one usually uses:
formail +1 -ds >>the_mailbox_of_your_choice
formail +1 -ds procmail
To remove all Received: fields from the header:
formail -I Received:
To remove all fields except From: and Subject: from the header:
formail -k -X From: -X Subject:
To supersede the Reply-To: field in a header you could use:
formail -i "Reply-To: foo@bar"
To convert a non-standard mailbox file into a standard mailbox file you
formail -ds <old_mailbox >>new_mailbox
Or, if you have a very tolerant mailer:
formail -a Date: -ds <old_mailbox >>new_mailbox
To extract the header from a message:
formail -X ""
sed -e '/^$/ q'
To extract the body from a message:
formail -I ""
sed -e '1,/^$/ d'
mail(1), sendmail(8), procmail(1), sed(1), sh(1), RFC822, RFC2822,
Can't fork Too many processes on this machine.
Content-Length: field exceeds actual length by nnn bytes
The Content-Length: field in the header
specified a length that was longer than the
actual body. This causes this message to absorb
a number of subsequent messages following it in
the same mailbox.
Couldn't write to stdout
The program that formail was trying to pipe into
didn't accept all the data formail sent to it;
this diagnostic can be suppressed by the -q
Duplicate key found: x The Message-ID or sender x in this message was
found in the idcache; this diagnostic can be
suppressed by the -q option.
Failed to execute "x" Program not in path, or not executable.
File table full Too many open files on this machine.
Invalid field-name: "x"
The specified field-name "x" contains control
characters, or cannot be a partial field-name
for this option.
You can save yourself and others a lot of grief if you try to avoid
using this autoreply feature on mails coming through mailinglists.
Depending on the format of the incoming mail (which in turn depends on
both the original sender's mail agent and the mailinglist setup)
formail could decide to generate an autoreply header that replies to
In the tradition of UN*X utilities, formail will do exactly what you
ask it to, even if it results in a non-RFC822 compliant message. In
particular, formail will let you generate header fields whose name ends
in a space instead of a colon. While this is correct for the leading
`From ' line, that line is not a header field so much as the message
separator for the mbox mailbox format. Multiple occurrences of such a
line or any other colonless header field will be considered by many
mail programs, including formail itself, as the beginning of a new
message. Others will consider the message to be corrupt. Because of
this, you should not use the -i option with the `From ' line as the
resulting renamed line, `Old-From ', will probably not do what you want
it to. If you want to save the original `From ' line, rename it with
the -R option to a legal header field such as `X-From_:'.
When formail has to generate a leading `From ' line it normally will
contain the current date. If formail is given the option `-a Date:',
it will use the date from the `Date:' field in the header (if present).
However, since formail copies it verbatim, the format will differ from
that expected by most mail readers.
If formail is instructed to delete or rename the leading `From ' line,
it will not automatically regenerate it as usual. To force formail to
regenerate it in this case, include -a 'From '.
If formail is not called as the first program in a pipe and it is told
to split up the input in several messages, then formail will not
terminate until the program it receives the input from closes its
output or terminates itself.
If formail is instructed to generate an autoreply mail, it will never
put more than one address in the `To:' field.
Formail is eight-bit clean.
When formail has to determine the sender's address, every RFC822
conforming mail address is allowed. Formail will always strip down the
address to its minimal form (deleting excessive comments and
The regular expression that is used to find `real' postmarks is:
"\n\nFrom [\t ]*[^\t\n ]+[\t ]+[^\n\t ]"
If a Content-Length: field is found in a header, formail will copy the
number of specified bytes in the body verbatim before resuming the
regular scanning for message boundaries (except when splitting digests
or Berkeley mailbox format is assumed).
Any header lines immediately following the leading `From ' line that
start with `>From ' are considered to be a continuation of the `From '
line. If instructed to rename the `From ' line, formail will change
each leading `>' into a space, thereby transforming those lines into
normal RFC822 continuations.
Calling up formail with the -h or -? options will cause it to display a
command-line help page.
This program is part of the procmail mail-processing-package (v3.22)
available at http://www.procmail.org/ or ftp.procmail.org in
There exists a mailinglist for questions relating to any program in the
for submitting questions/answers.
for subscription requests.
If you would like to stay informed about new versions and official
patches send a subscription request to
(this is a readonly list).
Stephen R. van den Berg
Philip A. Guenther