Linux.Desktop.Hacks [Electronic resources] نسخه متنی

Hack 59. Convert Your Mailbox

Don't let your old email
become stranded in a format that your new mail program
can't read.

Switching email clients, MTAs, or
mail servers can be a traumatic
process. And getting used to the different interface of an email
client and its way of working can be awkward. Aside from the cosmetic
changes, you might have a far more serious problem if the new client
stores its mail differently.

This hack takes you through the steps of converting between the two
most popular formats on Linux: mbox and
maildir. This can often be a daunting and
confusing process, but with this hack by your side, you will be
converting your mail in no time.

The most common reasons to switch mailbox formats are as follows:

Switching email clients

Not all email clients support both
mailbox formats. If
you really want to use a client that doesn't support
your current format, you need to covert your old mail to a format
that is supported.

Switching your local delivery agent

Many Linux users run an MTA on their desktops to handle mail delivery
to local users. Like email clients, not all email servers support
each mailbox format. When switching servers, it might be necessary to
convert your mail from one format to another.

Switching mail servers

This is like switching your local MTA, only on a larger scale. If you
administer users on a mail server, it might be necessary to convert
their mailboxes when you switch MTAs.

Generally, the mailbox format is dictated by the MTA, and you choose
your client accordingly. Of course, if you want a particular client
for its unique feature, you might need to switch (or reconfigure)
your MTA. You might also decide to switch between the two based
purely on technical merits, so here is a brief rundown of the
differences.

8.6.1. mbox Versus maildir

mbox is the older of the
two mail storage formats. It is
actually the generic name for a family of related formats. Although
the formats are slightly different, they both store multiple messages
within a single file. These multiple formats came about because of
different Mail User Agents (MUAs) implementing their own variations
of the original format. Although they are very similar, they are
generally not compatible between MUAs. Because of the single file
format, there can be problems with file-locking and storage on
networked filesystems such as NFS, which might cause the mail file to
be corrupted.

maildir, on the other hand, stores one message
per file. This removes the locking problems of
mbox, which means it should be your first choice
is your mail is stored over NFS. Because of its relative youth
compared to some of the MUAs that support it, there are no variants
of the format, so your mail should be portable between clients.

Generally, maildir is considered to be superior
to mbox.

8.6.2. Converting mbox to maildir

You can convert between the two formats with the
mb2md.pl Perl script, which you can find at
http://batleth.sapienti-sat.org/projects/mb2md.
To use this tool, you need to have both Perl and its
TimeDate module installed, but packages of the
script are available for various distributions that should take care
of these dependencies for you.

First, you need to know where your mail is coming from. Your
mbox mail is normally stored in two locations:
/var/spool/mail/$user for new mail and an
mbox file in your home folder for read mail,
although the paths and filenames can be distribution-dependent. If
you sort your mail into folders, each folder is represented by a
single file within your mail directory.

When run, mb2md.pl discovers your new and read
mail locations automatically, but you need to point it at any other
folders containing mbox files. If necessary, you
can also point it at specific files. The following examples assume
you've downloaded the script from its site.

To convert your new and read mail into a
newmaildir folder:

foo@bar:~$ perl mb2md.pl -m

To send the output to a different folder:

foo@bar:~$ perl mb2md.pl -m -d  somefolder

To tell it where to convert the files in a specific folder:

foo@bar:~$ perl mb2md.pl -s  sourcefolder

To convert the files in a folder recursively (for nested folders):

foo@bar:~$ perl mb2md.pl -s  sourcefolder  -R

8.6.3. Converting maildir to mbox

The main conversion
from maildir
to mbox is achieved in a much more hack-ish way,
by writing a small shell script that uses the
formail tool to filter input into
mbox format. Create a file called
md2mb.sh in you home folder, making sure you
replace maildir with your own mailbox. Insert the
following text into the file:

#!/bin/bash
for file in `find maildir/.$1/cur/ -type f`
do
cat $file | formail -a Date: >> mbox
done

Make the script executable with:

foo@bar:~$ chmod +x md2mb.sh

Then run it with:

foo@bar:~$ ./md2mb.sh

To process a particular folder, run it with:

foo@bar:~$ ./md2mb.sh 
foldername

This appends any email in the maildir folder to
an mbox file that can be read with
mail or your favorite MUA.

David Murphy