--- name: "mhfixmsg" section: "1mh" platform: "linux" package: "nmh" version: "1.8-3" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/mhfixmsg" --- # mhfixmsg(1mh) nmh's MIME-email rewriter with various transformations ## NAME mhfixmsg - nmh's MIME-email rewriter with various transformations ## SYNOPSIS **mhfixmsg** \[**-help**\] \[**-version**\] \[*+folder*\] \[*msgs* \| *absolute pathname* \| **-file** *file*\] \[**-decodetext** 8bit\|7bit\|binary \| **-nodecodetext**\] \[**-decodetypes** *type/\[subtype\]\[,...\]*\] \[**-decodeheaderfieldbodies** utf-8 \| **-nodecodeheaderfieldbodies**\] \[**-crlflinebreaks** \| **-nocrlflinebreaks**\] \[**-textcharset** *charset* \| **-notextcharset**\] \[**-reformat** \| **-noreformat**\] \[**-replacetextplain** \| **-noreplacetextplain**\] \[**-fixboundary** \| **-nofixboundary**\] \[**-fixcte** \| **-nofixcte**\] \[**-checkbase64** \| **-nocheckbase64**\] \[**-fixtype** *mimetype*\] \[**-outfile** *outfile*\] \[**-rmmproc** *program*\] \[**-normmproc**\] \[**-changecur** \| **-nochangecur**\] \[**-verbose** \| **-noverbose**\] ## DESCRIPTION **mhfixmsg** rewrites MIME messages, applying specific transformations such as decoding of MIME-encoded message parts and repairing invalid MIME headers. MIME messages are specified in RFC 2045 to RFC 2049 (see [*mhbuild*(1)](/mhbuild/1.md)). The **mhlist** command is invaluable for viewing the content structure of MIME messages. **mhfixmsg** passes non-MIME messages through without any transformations. If no transformations apply to a MIME message, the original message or file is not modified or removed. Thus, **mhfixmsg** can safely be run multiple times on a message. The **-decodetext** switch enables a transformation to decode each base64 and quoted-printable text message part to the selected 8-bit, 7-bit, or binary encoding. If 7-bit is selected for a base64 part but it will only fit 8-bit, as defined by RFC 2045, then it will be decoded to 8-bit quoted-printable. Similarly, with 8-bit, if the decoded text would be binary, then the part is not decoded (and a message will be displayed if **-verbose** is enabled). Note that **-decodetext** binary can produce messages that are not compliant with RFC 5322, §2.1.1. When the **-decodetext** switch is enabled, each carriage return character that precedes a linefeed character is removed from text parts encoded in ASCII, ISO-8859-x, UTF-8, or Windows-12xx. The **-decodetypes** switch specifies the message parts, by type and optionally subtype, to which **-decodetext** applies. Its argument is a comma-separated list of type/subtype elements. If an element does not contain a subtype, then **-decodetext** applies to all subtypes of the type. The default **-decodetypes** includes *text*; it can be overridden, e.g., with **-decodetypes** *text/plain* to restrict **-decodetext** to just text/plain parts. The **-decodeheaderfieldbodies** switch enables decoding of header field bodies to the specified character set. The **-nodecodeheaderfieldbodies** inhibits this transformation. The transformation can produce a message that does not conform with RFC 2047, §1, paragraph 6, because the decoded header field body could contain unencoded non-ASCII characters. It is therefore not enabled by default. Decoding of most header field bodies, or to a character set that is different from that of the user's locale, requires that **nmh** be built with [*iconv*(3)](/iconv/3.md); see [*mhparam*(1)](/mhparam/1.md) for how to determine whether your **nmh** installation includes that. By default, carriage return characters are preserved or inserted at the end of each line of text content. The **-crlflinebreaks** switch selects this behavior and is enabled by default. The **-nocrlflinebreaks** switch causes carriage return characters to be stripped from, and not inserted in, text content when it is decoded and encoded. Note that its use can cause the generation of MIME messages that do not conform with RFC 2046, §4.1.1, paragraph 1. The **-textcharset** switch specifies that all text/plain parts of the message(s) should be converted to *charset*. Charset conversions require that **nmh** be built with [*iconv*(3)](/iconv/3.md); see [*mhparam*(1)](/mhparam/1.md) for how to determine whether your **nmh** installation includes that. To convert text parts other than text/plain, an external program can be used, via the **-reformat** switch. The **-textcharset** switch can also be used, depending on the **nmh** installation as described below, to specify the Content-Type charset parameter for text/plain parts added with **-reformat**. The **-reformat** switch enables a transformation for text parts in the message. For each text part that is not text/plain and that does not have a corresponding text/plain in a multipart/alternative part, **mhfixmsg** looks for a mhfixmsg-format-text/subtype profile entry that matches the subtype of the part. If one is found and can be used to successfully convert the part to text/plain, **mhfixmsg** inserts that text/plain part at the beginning of the containing multipart/alternative part, if present. If not, it creates a multipart/alternative part. With the **-reformat** switch, multipart/related parts are handled differently than multipart/alternative. If the multipart/related has only a single part that is not text/plain and can be converted to text/plain, a text/plain part is added and the type of the part is changed to multipart/alternative. If the multipart/related has more than one part but does not have a text/plain part, **mhfixmsg** tries to add one. The **-replacetextplain** switch broadens the applicability of **-reformat**, by always replacing a corresponding text/plain part, if one exists. If **-verbose** is enabled, the replacement will be shown as two steps: a removal of the text/plain part, followed by the usual insertion of a new part. **-reformat** requires a profile entry for each text part subtype to be reformatted. The mhfixmsg-format-text/subtype profile entries are based on external conversion programs, and are used in the same way that **mhshow** uses its mhshow-show-text/subtype entries. When **nmh** is installed, it searches for a conversion program for text/html content, and if one is found, inserts a mhfixmsg-format-text/html entry in /etc/nmh/mhn.defaults. An entry of the same name in the user's profile takes precedence. The user can add entries for other text subtypes to their profile. The character set (charset) of text/plain parts added by **-reformat** is determined by the external program that generates the content. Detection of the content charset depends on how the **nmh** installation was configured. If a program, such as **file** with a **--mime-encoding** option, was found that can specify the charset of a file, then that will be used for the Content-Type charset parameter. To determine if your **nmh** was so configured, run **mhparam mimeencodingproc** and see if a non-empty string is displayed. If your **nmh** was not configured with a program to determine the charset of a file, then the value of the **-textcharset** switch is used. It is up to the user to ensure that the **-textcharset** value corresponds to the character set of the content generated by the external program. The **-fixboundary** switch enables a transformation to repair the boundary portion of the Content-Type header field of the message to match the boundaries of the outermost multipart part of the message, if it does not. That condition is indicated by a “bogus multipart content in message” error message from **mhlist** and other **nmh** programs that parse MIME messages. The **-fixcte** switch enables a transformation to change the Content-Transfer-Encoding from an invalid value to 8-bit in message parts with a Content-Type of multipart and message, as required by RFC 2045, §6.4. That condition is indicated by a “must be encoded in 7bit, 8bit, or binary” error message from **mhlist** and other **nmh** programs that parse MIME messages. The **-checkbase64** switch enables a check of the encoding validity in base64-encoded MIME parts. The check looks for a non-encoded text footer appended to a base64-encoded part. Per RFC 2045 §6.8, the occurrence of a "=" character signifies the end of base-64 encoded content. If none is found, a heuristic is used: specifically, two consecutive invalid base64 characters signify the beginning of a plain text footer. If a text footer is found and this switch is enabled, **mhfixmsg** separates the base64-encoded and non-encoded content and places them in a pair of subparts to a newly constructed multipart/mixed part. That multipart/mixed part replaces the original base64-encoded part in the MIME structure of the message. The **-fixtype** switch ensures that each part of the message has the correct MIME type shown in its Content-Type header. It may be repeated. It is typically used to replace “application/octet-stream” with a more descriptive MIME type. It may not be used for multipart and message types. **mhfixmsg** applies two transformations unconditionally. The first removes an extraneous trailing semicolon from the parameter lists of MIME header field values. The second replaces RFC 2047 encoding with RFC 2231 encoding of name and filename parameters in Content-Type and Content-Disposition header field values, respectively. The **-verbose** switch directs **mhfixmsg** to output informational message for each transformation applied. The return status of **mhfixmsg** is 0 if all of the requested transformations are performed, or non-zero otherwise. (**mhfixmsg** will not decode to binary content with the default **-decodetext** setting, but a request to do so is not considered a failure, and is noted with **-verbose**.) If a problem is detected with any one of multiple messages such that the return status is non-zero, then none of the messages will be modified. The **-file** *file* switch directs **mhfixmsg** to use the specified file as the source message, rather than a message from a folder. Only one file argument may be provided. The **-file** switch is implied if *file* is an absolute pathname. If the file is “-”, then **mhfixmsg** accepts the source message on the standard input stream. If the **-outfile** switch is not enabled when using the standard input stream, **mhfixmsg** will not produce a transformed output message. **mhfixmsg**, by default, transforms the message in place. If the **-outfile** switch is enabled, then **mhfixmsg** does not modify the input message or file, but instead places its output in the specified file. An outfile name of “-” specifies the standard output stream. Combined with the **-verbose** switch, the **-outfile** switch can be used to show what transformations **mhfixmsg** would apply without actually applying them, e.g., mhfixmsg -outfile /dev/null -verbose As always, this usage obeys any **mhfixmsg** switches in the user's profile. **-outfile** can be combined with **rcvstore** to add a single transformed message to a different folder, e.g., mhfixmsg -outfile - \| \\ /usr/lib/mh/rcvstore +folder ### Summary of Applicability The transformations apply to the parts of a message depending on content type and/or encoding as follows: ``` -decodetext base64 and quoted-printable encoded text parts -decodetypes limits parts to which -decodetext applies -decodeheaderfieldbodies all message parts -crlflinebreaks text parts -textcharset text/plain parts -reformat text parts that are not text/plain -fixboundary outermost multipart part -fixcte multipart or message part -checkbase64 base64 encoded parts -fixtype all except multipart and message parts ``` ### Backup of Original Message/File If it applies any transformations to a message or file, and the **-outfile** switch is not used, **mhfixmsg** backs up the original the same way as **rmm**. That is, it uses the *rmmproc* profile component, if present. If not present, **mhfixmsg** moves the original message to a backup file. The **-rmmproc** switch may be used to override this profile component. The **-normmproc** switch disables the use of any *rmmproc* profile component and negates all prior **-rmmproc** switches. ### Integration with inc **mhfixmsg** can be used as an add-hook, as described in /usr/share/doc/nmh/README-HOOKS. Note that add-hooks are called from all **nmh** programs that add a message to a folder, not just **inc**. Alternatively, a simple shell alias or function can be used to call **mhfixmsg** immediately after a successful invocation of **inc**. One approach could be based on: msgs=\`inc -format '%(msg)'\` && \[ -n "$msgs" \] && scan $msgs && mhfixmsg -nochangecur $msgs Another approach would rely on adding a sequence to Unseen-Sequence, which **inc** sets with the newly incorporated messages. Those could then be supplied to **mhfixmsg**. An example is shown below. ### Integration with procmail By way of example, here is an excerpt from a procmailrc file that filters messages through **mhfixmsg** before storing them in the user's *nmh-workers* folder. It also stores the incoming message in the *Backups* folder in a filename generated by **mkstemp**, which is a non-POSIX utility to generate a temporary file. Alternatively, **mhfixmsg** could be called on the message after it is stored. ``` PATH = /usr/bin/mh:$PATH LANG = en_US.utf8 MAILDIR = `mhparam path` #### The Backups directory is relative to MAILDIR. MKSTEMP = 'mkstemp -directory Backups -prefix mhfixmsg' MHFIXMSG = 'mhfixmsg -noverbose -file - -outfile -' STORE = /usr/lib/mh/rcvstore :0 w: nmh-workers/procmail.$LOCKEXT * ^TOnmh-workers@nongnu.org | tee `$MKSTEMP` | $MHFIXMSG | $STORE +nmh-workers ``` ## EXAMPLES ### Basic usage To run **mhfixmsg** on the current message in the current folder, with default transformations to fix MIME boundaries and Content-Transfer-Encoding, to decode text and application/ics content parts to 8 bit, and to add a corresponding text/plain part where lacking: ``` mhfixmsg -verbose ``` ### Specified folder and messages To run **mhfixmsg** on specified messages, without its informational output: ``` mhfixmsg +inbox last:4 ``` ### View without modification By default, **mhfixmsg** transforms the message in place. To view the MIME structure that would result from running **mhfixmsg** on the current message, without modifying the message: ``` mhfixmsg -outfile - | mhlist -file - ``` ### Search message without modification To search the current message, which possibly contains base64 or quoted printable encoded text parts, without modifying it, use the **-outfile** switch: ``` mhfixmsg -outfile - | grep pattern ``` **-outfile** can be abbreviated in usual MH fashion, e.g., to -o. The search will be on the entire message, not just text parts. ### Translate text/plain parts to UTF-8 To translate all text/plain parts in the current message to UTF-8, in addition to all of the default transformations: ``` mhfixmsg -textcharset utf-8 ``` ### Fix all messages in a folder To run **mhfixmsg** on all of the messages in a folder: ``` mhfixmsg +folder all ``` Alternatively, **mhfixmsg** can be run on each message separately, e.g., using a Bourne shell loop: ``` for msg in `pick +folder`; do mhfixmsg +folder $msg; done ``` The two appearances of the **+folder** switch in that command protect against concurrent context changes by other **nmh** command invocations. ### Run on newly incorporated messages To run **mhfixmsg** on messages as they are incorporated: ``` inc && mhfixmsg -nochangecur unseen ``` This assumes that the Unseen-Sequence profile entry is set to **unseen**, as shown in [*mh-profile*(5)](/mh-profile/5.md). ## FILES **mhfixmsg** looks for mhn.defaults in multiple locations: absolute pathnames are accessed directly, tilde expansion is done on usernames, and files are searched for in the user's *Mail* directory as specified in their profile. If not found there, the directory “*/etc/nmh*” is checked. ``` ^$HOME/.mh_profile~^The user profile ^/etc/nmh/mhn.defaults~^Default mhfixmsg conversion entries ``` ## PROFILE COMPONENTS ``` ^Path:~^To determine the user's nmh directory ^Current-Folder:~^To find the default current folder ^rmmproc:~^Program to delete original messages or files ``` ## SEE ALSO [*iconv*(3)](/iconv/3.md), [*inc*(1)](/inc/1.md), *mh-mkstemp*(1), [*mh-profile*(5)](/mh-profile/5.md), [*mhbuild*(1)](/mhbuild/1.md), [*mhlist*(1)](/mhlist/1.md), [*mhparam*(1)](/mhparam/1.md), [*mhshow*(1)](/mhshow/1.md), [*procmail*(1)](/procmail/1.md), [*procmailrc*(5)](/procmailrc/5.md), [*rcvstore*(1)](/rcvstore/1.md), [*rmm*(1)](/rmm/1.md) ## DEFAULTS ``` `+folder' defaults to the current folder `msgs' defaults to cur `-decodetext 8bit' `-decodetypes text,application/ics' `-nodecodeheaderfieldbodies' `-crlflinebreaks' `-notextcharset' `-reformat' `-noreplacetextplain' `-fixboundary' `-fixcte' `-checkbase64' `-changecur' `-noverbose' ``` ## CONTEXT If a folder is given, it will become the current folder. The last message selected from a folder will become the current message, unless the **-nochangecur** switch is enabled. If the **-file** switch or an absolute pathname is used, the context will not be modified.