Compressed Folders Feature

Read from/write to compressed mailboxes

1. Support

Since: NeoMutt 2016-05-30

Dependencies: None

2. Introduction

The Compressed Folder feature allows NeoMutt to read mailbox files that are compressed. But it isn't limited to compressed files. It works well with encrypted files, too. In fact, if you can create a program/script to convert to and from your format, then NeoMutt can read it.

The feature adds three hooks to NeoMutt: open-hook, close-hook and append-hook. They define commands to: uncompress a file; compress a file; append messages to an already compressed file.

There are some examples of both compressed and encrypted files, later. For now, the documentation will just concentrate on compressed files.

3. Commands

open-hook pattern shell-command
close-hook pattern shell-command
append-hook pattern shell-command

The shell-command must contain two placeholders for filenames: %f and %t. These represent from and to filenames. These placeholders should be placed inside single-quotes to prevent unintended shell expansions.

If you need the exact string %f or %t in your command, simply double up the % character, e.g. %%f or %%t.

Table 9.1. Not all Hooks are Required

Open Close Append Effect Useful if
Open - - Folder is readonly The folder is just a backup
Open Close - Folder is read/write, but the entire folder must be written if anything is changed Your compression format doesn't support appending
Open Close Append Folder is read/write and emails can be efficiently added to the end Your compression format supports appending
Open - Append Folder is readonly, but can be appended to You want to store emails, but never change them

Note

The command:

  • should return a non-zero exit status on failure

  • should not delete any files

3.1. Read from compressed mailbox

open-hook regexp shell-command

If NeoMutt is unable to open a file, it then looks for open-hook that matches the filename.

If your compression program doesn't have a well-defined extension, then you can use .as the regexp.

3.1.1. Example of open-hook

open-hook '\.gz$' "gzip --stdout --decompress '%f' > '%t'"
  • NeoMutt finds a file, example.gz, that it can't read

  • NeoMutt has an open-hook whose regexp matches the filename: \.gz$

  • NeoMutt uses the command gzip -cd to create a temporary file that it can read

3.2. Write to a compressed mailbox

close-hook regexp shell-command

When NeoMutt has finished with a compressed mail folder, it will look for a matching close-hook to recompress the file. This hook is optional.

Note

If the folder has not been modified, the close-hook will not be called.

3.2.1. Example of close-hook

close-hook '\.gz$' "gzip --stdout '%t' > '%f'"
  • NeoMutt has finished with a folder, example.gz, that it opened with open-hook

  • The folder has been modified

  • NeoMutt has a close-hook whose regexp matches the filename: \.gz$

  • NeoMutt uses the command gzip -c to create a new compressed file

Note

The close-hook can also include extra options, e.g. compression level: --best

3.3. Append to a compressed mailbox

append-hook regexp shell-command

When NeoMutt wants to append an email to a compressed mail folder, it will look for a matching append-hook. This hook is optional.

Using the append-hook will save time, but NeoMutt won't be able to determine the type of the mail folder inside the compressed file.

NeoMutt will assume the type to be that of the $mbox_type variable. NeoMutt also uses this type for temporary files.

NeoMutt will only use the append-hook for existing files. The close-hook will be used for empty, or missing files.

Note

If your command writes to stdout, it is vital that you use >>in the append-hook. If not, data will be lost.

3.3.1. Example of append-hook

append-hook '\.gz$' "gzip --stdout '%t' >> '%f'"
  • NeoMutt wants to append an email to a folder, example.gz, that it opened with open-hook

  • NeoMutt has an append-hook whose regexp matches the filename: \.gz$

  • NeoMutt knows the mailbox type from the $mbox variable

  • NeoMutt uses the command gzip -c to append to an existing compressed file

Note

The append-hook can also include extra options, e.g. compression level: --best

3.4. Empty Files

NeoMutt assumes that an empty file is not compressed. In this situation, unset $save_empty, so that the compressed file will be removed if you delete all of the messages.

3.5. Security

Encrypted files are decrypted into temporary files which are stored in the $tmpdir directory. This could be a security risk.

4. neomuttrc

# Example NeoMutt config file for the compress feature.

# This feature adds three hooks to NeoMutt which allow it to
# work with compressed, or encrypted, mailboxes.

# The hooks are of the form:
#       open-hook   regexp "shell-command"
#       close-hook  regexp "shell-command"
#       append-hook regexp "shell-command"
# The 'append-hook' is optional.

# Handler for gzip compressed mailboxes
open-hook   '\.gz$' "gzip --stdout --decompress '%f' >  '%t'"
close-hook  '\.gz$' "gzip --stdout              '%t' >  '%f'"
append-hook '\.gz$' "gzip --stdout              '%t' >> '%f'"
# Handler for bzip2 compressed mailboxes
open-hook   '\.bz2$' "bzip2 --stdout --decompress '%f' >  '%t'"
close-hook  '\.bz2$' "bzip2 --stdout              '%t' >  '%f'"
append-hook '\.bz2$' "bzip2 --stdout              '%t' >> '%f'"
# Handler for xz compressed mailboxes
open-hook   '\.xz$' "xz --stdout --decompress '%f' >  '%t'"
close-hook  '\.xz$' "xz --stdout              '%t' >  '%f'"
append-hook '\.xz$' "xz --stdout              '%t' >> '%f'"
# Handler for pgp encrypted mailboxes
# PGP does not support appending to an encrypted file
open-hook   '\.pgp$' "pgp -f < '%f' > '%t'"
close-hook  '\.pgp$' "pgp -fe YourPgpUserIdOrKeyId < '%t' > '%f'"
# Handler for gpg encrypted mailboxes
# gpg does not support appending to an encrypted file
open-hook   '\.gpg$' "gpg --decrypt < '%f' > '%t'"
close-hook  '\.gpg$' "gpg --encrypt --recipient YourGpgUserIdOrKeyId < '%t' > '%f'"


# vim: syntax=neomuttrc

6. Credits