Email with nmh and other command-line programs¶

Introduction ¶

I have a few email accounts that offer POP3 access and I send my emails via the SMTP server of my internet service provider.

I’m a happy Claws Mail user on my Debian GNU/Linux box, but I’m interested in being able to manage email via command-line programs. Claws Mail stores mails in the so called MH mailbox format. This mailbox format is the one of the MH Message Handling System, a command-line based mail handling system.

nmh is the current implementation of the MH system (provided by package nmh on a Debian GNU/Linux system). It is possible to use both Claws Mail and nmh.

This page gives the various actions I had to take to be able to receive and send emails using the nmh command-line programs. Filtering the incoming messages with Bogofilter (anti-spam filter) is also covered. Some basic commands for message management (deletion, search) are also provided. Of course, nmh programs have many options that are not covered here. Please refer to the nmh man pages for all the details.

Installation ¶

On a Debian GNU/Linux system, install fetchmail and nmh (as root) with:

apt-get install fetchmail nmh mh-book # As root.

The nmh programs are installed in /usr/bin/mh. This directory is not in the search path by default. You can add it to the search path by adding this line to a startup file (e.g. ~/.profile, .xsessionrc):

PATH="$PATH:/usr/bin/mh"

This makes it possible to invoke the nmh programs by their base name (e.g. inc) instead of their full path (e.g. /usr/bin/mh/inc).

If exim4 is not already installed, install it (as root) with:

apt-get install exim4 # As root.

Configuration ¶

Exim4 ¶

Configure Exim4 (as root) with:

dpkg-reconfigure exim4-config # As root.

I gave the following answers:

General type of mail configuration:: mail sent by smarthost; received via SMTP or fetchmail
System mail name:: Default value (<my_hostname>.<my_local_domain_name>)
IP-addresses to listen on for incoming SMTP connections:: Default value (127.0.0.1 ; ::1)
Other destinations for which mail is accepted:: Default value (<my_hostname>.<my_local_domain_name>)
Machine to relay mail for:: Default value (empty)
IP address or host name of the outgoing smarthost:: <smtp_server_host_name> (like “smtp.my_isp.xxx”)
Hide local mail name in outgoing mail:: Yes
Visible domain name for local users:: <valid_mail_domain> (like “my_isp.xxx”)
Keep number of DNS-queries minimal (Dial-on-demand):: Default value (no) (note: I have a permanent internet connection)
Delivery method for local mail:: mbox format in /var/mail/
Split configuration into small files:: Default value (no)

As a test, I issued the following command which is supposed to send a mail containing “Test” to a recipient. The -v switch is for verbosity. I notice that the mails that I send that way are not delivered to all recipients. So there must be something wrong. I don’t know what exactly, probably something that makes those mails appear as spam to certain filter programs:

/usr/sbin/sendmail -v recipient@example.com
Test
.

/usr/sbin/sendmail is a symbolic link to exim4 executable.

You can specify the “from” address using a -f switch on the command line and specify the mail subject by starting the message with a subject: line:

/usr/sbin/sendmail -f sender@example.com -v recipient@example.com
subject:The subject
The mail body.
.

fetchmail ¶

Create a ~/.fetchmailrc file and change its permission so that only the user can read and write it:

chmod 600 ~/.fetchmailrc

You can download an example .fetchmailrc file. The SSL related options may not be needed in all cases (see Debian bug #922164).

nmh user installation ¶

Perform nmh user installation with:

/usr/bin/mh/install-mh

Retrieving mails ¶

Without any filtering ¶

Run the two following commands to retrieve mails:

fetchmail       # Retrieves new mails.
/usr/bin/mh/inc # Incorporates retrieved mails to the inbox folder of the nmh
                # directory.

With filtering by Bogofilter ¶

Make sure procmail and bogofilter are installed:

apt-get install procmail bogofilter # As root.

Create a ~/.procmailrc like this example .procmailrc file and when invoking fetchmail, use the --mda option:

fetchmail --mda "procmail -f %F"

This results in the messages classified as spam being moved automatically to the “Spam” subdirectory of your nmh directory, and messages classified as unsure to the “Unsure spam” subdirectory.

Note the “slash dot” after the subdirectory names in the ~/.procmailrc file. That’s how procmail knows that we’re talking MH subdirectories. See here: https://unix.stackexchange.com/a/336422

And also, don’t forget to train Bogofilter!

Sending a mail ¶

Use /usr/bin/mh/comp. This program opens the text editor (on my Debian GNU/Linux system at least, on other system it may just launch /usr/bin/mh/prompter) so that you can edit the message draft. Save and quit when you are done. You’ll then get a prompt. Just hit “Enter” to see the list of available commands. One of these commands is “send”.

By default, /etc/nmh/components is used as message template. If your nmh directory is /home/my_user_name/Mail, you can put a custom components file there. It will be used automatically by /usr/bin/mh/comp. You can download an example components file with sender's name, address and signature.

To force /usr/bin/mh/comp to use a specific message template, use the -form switch:

/usr/bin/mh/comp -form path/to/components/file

To send a message that has already been prepared and saved in a file, use /usr/bin/mh/send:

/usr/bin/mh/send path/to/message/file

nmh also offers other programs to send mails: repl (to reply to a message) and forw (to forward a message) for example. They don’t use the same message templates as comp. repl uses /etc/nmh/replcomps and forw uses /etc/nmh/forwcomps.

Message management ¶

This section provides a few examples of commands you can use to manage the messages in your MH mailbox with nmh. Please keep in mind that nmh message management programs operate by default on the current folder. You can set the current folder with the folder program:

/usr/bin/mh/folder +'any folder' # Selects folder "any folder" as the current
                                 # folder.

/usr/bin/mh/folder +any/folder   # Selects folder "any/folder" subfolder as
                                 # the current folder.

/usr/bin/mh/folder +./any/folder # Selects folder "any/folder" subfolder as
                                 # the current folder (valid if the current
                                 # working directory is the MH mailbox).

folder without arguments simply indicates the current folder:

/usr/bin/mh/folder

You can force an nmh program to operate on a specific folder by providing this folder as argument (prepended with a plus sign). Note that with most nmh programs, this causes this folder to be selected as the current folder for the subsequent commands.

Note also that when no message (or message sequence) is provided on the command line, an nmh program operates on the current message or on all messages in the current folder. The nmh man pages state clearly what the default message (or message sequence) is for each program.

Deleting mails ¶

You can delete the mail with number 421 in the “Sent” folder with:

/usr/bin/mh/rmm +Sent 421

This does not really delete the mail, but renames it to “,421”. You may want to periodically erase your deleted mails with a command like:

find /home/my_user_name/Mail -name ,* -exec rm -f {} \;

Searching for recent messages ¶

You can search for recent messages with commands like:

/usr/bin/mh pick -after 5/15/2019 # Searches for messages dated May 5th, 2019
                                  # or later.

/usr/bin/mh pick -after -8        # Searches for messages not older than 8
                                  # days.

I couldn’t find a way of finding messages recursively (i.e. in all folders and subfolders) with nmh programs, but the find command can help here (it is assumed that the current working directory is the MH mailbox):

find . -mindepth 1 -type d -exec sh -c \
    '/usr/bin/mh/pick +"$1" -after -8 2>/dev/null \
    && echo "This was for $1"' - {} \;

Training Bogofilter (anti-spam filter)¶

Assuming that:

Your current working directory is your MH mailbox,
Your spam messages are in the “Spam” folder,
Your trash folder (if any) is empty,
You also have an “Unsure spam” folder that contains only spam messages (which implies that you have moved any ham (non spam) message away from this folder with (for example) commands like /usr/bin/mh/refile 1 -src +'Unsure spam' +'Any ham folder'),

you can move the messages in ‘Unsure spam’ to Spam and (re)train Bogofilter with the following commands:

rm -rf ~/.bogofilter                 # Don't do this if you don't want to
                                     # entirely reset the training.

refile all -src +'Unsure spam' +Spam # Moves the messages in 'Unsure spam' to
                                     # Spam.

rm 'Unsure spam'/*                   # Actually delete files in 'Unsure spam'

bogofilter -vsB Spam                 # Registers spam messages.

find . -mindepth 1 \
       -type d \
       -not -path "\./Spam" \
  | bogofilter -vnb                  # Registers ham messages.

You can check in which category (spam (S), ham (H), unsure (U)) Bogofilter classifies a message with commands like:

bogofilter -tB Spam/1

Such commands output one line. The first character of the line is S, H or U.