Under Development
stars

Compress Mailboxes

Compress Mailboxes#

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.

Commands#

open-hook   regex "shell-command"
close-hook  regex "shell-command"
append-hook regex "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.

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

Read from compressed mailbox#

open-hook regex "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 regex.

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 regex matches the filename: \.gz$

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

Write to a compressed mailbox#

close-hook regex "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.

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 regex 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

Append to a compressed mailbox#

append-hook regex "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.

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 regex 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

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.

Security#

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

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   regex "shell-command"
#       close-hook  regex "shell-command"
#       append-hook regex "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: filetype=neomuttrc

See Also#