Compresses email in maildir format

dovecot-maildir-compress.sh

#!/bin/sh

# Find the mails you want to compress in a single maildir.
#
#     Skip files that don't have ,S=<size> in the filename. 
#
# Compress the mails to tmp/
#
#     Update the compressed files' mtimes to be the same as they were in the original files (e.g. touch command) 
#
# Run maildirlock <path> <timeout>. It writes PID to stdout, save it.
#
#     <path> is path to the directory containing Maildir's dovecot-uidlist (the control directory, if it's separate)
# 
#     <timeout> specifies how long to wait for the lock before failing. 
#
# If maildirlock grabbed the lock successfully (exit code 0) you can continue.
# For each mail you compressed:
#
#     Verify that it still exists where you last saw it.
#     If it doesn't exist, delete the compressed file. Its flags may have been changed or it may have been expunged. This happens rarely, so just let the next run handle it.
#
#     If the file does exist, rename() (mv) the compressed file over the original file.
#
#         Dovecot can now read the file, but to avoid compressing it again on the next run, you'll probably want to rename it again to include e.g. a "Z" flag in the file name to mark that it was compressed (e.g. 1223212411.M907959P17184.host,S=3271:2,SZ). Remember that the Maildir specifications require that the flags are sorted by their ASCII value, although Dovecot itself doesn't care about that. 
#
# Unlock the maildir by sending a TERM signal to the maildirlock process (killing the PID it wrote to stdout). 

##
## <http://ivaldi.nl/blog/2011/12/06/compressed-mail-in-dovecot/>
##

store=/tmp/mail/srv/mail
compress=gzip
#compress=bzip2

find "$store" -type d -name "cur" | while read maildir;
do
    tmpdir=$(cd "$maildir/../tmp" &>/dev/null && pwd) || exit 1

    find=$(find "$maildir" -type f -name "*,S=*" -mtime +30 ! -name "*,*:2,*,*Z*" -printf "%f\n")

    if [ -z "$find" ];
    then
        continue
    fi

    echo "Before compression:"
    du -b "$maildir"

    echo "$find" | while read filename;
    do
        srcfile="$maildir/$filename"
        tmpfile="$tmpdir/$filename"

        $compress --best --stdout "$srcfile" > "$tmpfile" &&

        # Copy over some things
        chown --reference="$srcfile" "$tmpfile" &&
        chmod --reference="$srcfile" "$tmpfile" &&
        touch --reference="$srcfile" "$tmpfile"
    done

    # Should really check dovecot-uidlist is in $maildir/..
    if lock=$(/usr/lib/dovecot/maildirlock "$maildir/.." 10);
    then
        # The directory is locked now

        echo "$find" | while read filename;
        do
            flags=$(echo $filename | awk -F:2, '{print $2}')

            if echo $flags | grep ',';
            then
                newname=$filename"Z"
            else
                newname=$filename",Z"
            fi

            srcfile=$maildir/$filename
            tmpfile=$tmpdir/$filename
            dstfile=$maildir/$newname

            if [ -f "$srcfile" ] && [ -f "$tmpfile" ];
            then
                #echo "$srcfile -> $dstfile"

                mv "$tmpfile" "$srcfile" &&
                mv "$srcfile" "$dstfile"
            else
                rm -f "$tmpfile"
            fi
        done

        kill -s SIGTERM $lock

        echo "After compression:"
        du -b "$maildir"

        find "$maildir" -type f -name dovecot.index\* -delete
    else
        echo "Failed to lock: $maildir" >&2

        echo "$find" | while read filename;
        do
            rm -f "$tmpdir/$filename"
        done
    fi
done

Updates from the forked parent:

• output before and after directory sizes to show space savings
• kill command uses Debian/Ubuntu syntax
• added code to delete Dovecot indices for the affected diretories, as per comment.

Is is possible to calculate and add ,S=<size> to the filename? Should that just be the number of bytes?