Mutt has a powerful feature to dig into the history: the limit feature. By pressing l it is then possible to write a query to filter the mails. It is comparable to the WHERE part of a SQL statement and allow combining AND operators. In particular the ~b predicate allow to search within the email's body and the ~X lets filter attachments.

However that feature acts as a grep command and parse all the mails one by one. Searching in multiple dozen of thousand emails can last dozen of minutes. Here comes the notmuch program, that improves greatly the limit feature with instant search and some other goodies (and also drawbacks). The secret of this speed is it scan emails and produces a full text index to be used later.

The installation is straightforward on ubuntu with sudo apt install notmuch. The configuration is also piece of cake: notmuch config will setup the maildir folder. Later the notmuch new command allows to the mails and can be run again when new mails arrive. There is also a way to automatize the indexation by setup system notifications right there.

The integration in mutt to replace the limit feature only need the two rows below in the .muttrc configuration file. Pressing L will propose to write a query to filter the mails based on the index more information here. To get the full details on how to search within notmuch: man notmuch-search-index describes the syntax of the search.

# 'L' performs a notmuch query, showing only the results
macro index L "<enter-command>unset wait_key<enter><shell-escape>read -p 'notmuch query: ' x; echo \$x >~/.cache/mutt_terms<enter><limit>~i \"\`notmuch search --output=messages \$(cat ~/.cache/mutt_terms) | head -n 600 | perl -le '@a=<>;chomp@a;s/\^id:// for@a;s/\\+/\\\\+/g for@a;s/=/\\\\=/g for@a;$,=\"|\";print@a'\`\"<enter>" "show only messages matching a notmuch pattern"
# 'a' shows all messages again (supersedes default <alias> binding)
macro index a "<limit>all\n" "show all messages (undo limit)"

There is some caveats with notmuch however. Its search within attachment is not as powerfull as the built-in mutt. In particular, the later allows to specify the number of attachments. Last but not least, notmuch does only provide a stemmer for english. That's might be possible to extend it with an existing implementation of the french snowball parser.

# Install
sudo apt install maildir-utils

# Index Maildir
mu index -m my/maildir

# setup in crontab or use inotify service

# to add to .muttrc
# Mode 1.
#
# this allows to search into all mailbowes at once
# however, it is a readonly mailbox because off symlinks
macro index <F8> "<shell-escape>mu find --clearlinks --format=links --linksdir=~/Maildir/search "   "mu find"
macro index <F9> "<change-folder-readonly>~/Maildir/search"      "mu find results"

# Mode 2.
#
# this allows to show the 600 first emails
# it is
macro index L "<enter-command>unset wait_key<enter><shell-escape>read -p 'mu query: ' x; echo \$x >~/.cache/mutt_terms<enter><limit>~i \"\`mu find --fields i --quiet 2> /dev/null \$(cat ~/.cache/mutt_terms) | head -n 600 | perl -le '@a=<>;chomp@a;s/\^id:// for@a;s/\\+/\\\\+/g for@a;s/=/\\\\=/g for@a;$,=\"|\";print@a'\`\"<enter>" "show only messages matching a mu pattern"
# 'a' shows all messages again (supersedes default <alias> binding)
macro index a "<limit>all\n" "show all messages"