About me: My name is Solène Rapenne, pronouns she/her. I like learning and sharing knowledge. Hobbies: '(BSD OpenBSD h+ Lisp cmdline gaming internet-stuff). I love percent and lambda characters. OpenBSD developer solene@.

Contact me: solene on Freenode, solene+www at dataswamp dot org or solene@bsd.network (mastodon). If for some reason you want to give me some money, I accept paypal at the address donate@perso.pw.

Full featured Slackware email server with sendmail and cyrus-imapd

Written by Solène, on 14 November 2020.
Tags: #slackware #email

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This article is about making your own mail server using Slackware linux distribution, sendmail and cyrus-imap. This choice is because I really love Slackware and I also enjoy non-mainstream stacks. While everyone would recommend postfix/dovecot, I prefer using sendmail/cyrus-imap. Please not this article contain ironical statements, I will try to write them with some emphasis.

While some people use fossil fuel cars, some people use Slackware.

If you are used to clean, reproducible and automated deployments, the present how-to is the totally opposite. This is the /Slackware/ way.


Slackware is one of the oldest (maybe the oldest with debian) linux distribution out there and it’s still usable. The last release (14.2) is 4 years old but there are still security updates. I choose to use the development branch slackware-current for this article.

I discovered an alternative to Windows in the early 2000’ with a friend showing me a « Linux » magazine, featuring Slackware installation CDs and the instructions to install. It was my very first contact with Linux and open source ever. I used Slackware multiple times over time, and it was always a great system for me on my main laptop.

The Slackware specifics could be said as: “not changing much” and “quite limited”. Slackware never change much between releases, from 2010 to 2020, it’s pretty much the same system when you use it. I say it’s rather limited, package wise, the default Slackware installation requires like 15 GB on your disk because it bundles KDE and all the kde apps, a bunch of editors (emacs,vim,vs,elvis), lot of compilers/interpreter (gcc, llvm, ada, scheme, python, ruby etc..). While it provides a LOT of things out of the box, you really get all Slackware can offer. If something isn’t in the packages, you need to install it yourself.

Full Disk Encryption or nothing

I recommend to EVERYONE the practice of having a full disk encryption (phone, laptop, workstation, servers). If your system get stolen, you will only lose hardware when you use full disk encryption.

Without encryption, the thief can access all your data forever.

Slackware provides a file README_CRYPT.txt explaining how to install on an encrypted partition. Don’t forget to tell the bootloader LILO about the initrd, and keep in mind the initrd must be recreated after kernel upgrade

Use ntpd

It’s important to have a correct time on your server.

# chmod +x /etc/rc.d/rc.ntpd
# /etc/rc.d/rc.ntpd start

Disable ssh password authentication

In /etc/ssh/sshd_config there are two changes to do:

Turn UsePam yes into UsePam no and add PasswordAuthentication.

Changes can be applied by restarting ssh with /etc/rc.d/rc.sshd restart.

Before enabling this, don’t forget to deploy your public key to an user who is able to become to root.

Get a SSL certificate

We need a SSL certificate for the infrastructure, so we will install certbot. Unfortunately, certbot-auto doesn’t work on Slackware because the system is unsupported. So we will use pip and call certbot in standalone mode so we don’t need a web server.

# pip3 install certbot
# certbot certonly --standalone -d mydomain.foobar -m usernam@example

My domain being kongroo.eu the files are generated under /etc/letsencrypt/live/kongroo.eu/.

Configure the DNS

Three DNS entries have to be added for a working email server.

  1. SPF to tell the world which addresses have the right send your emails
  2. MX to tell the world which addresses will receive the emails and in which order
  3. DKIM (a public key) to allow recipients to check your emails really comes from your servers (signed used a private key)
  4. DMARC to tell recipient what to do with mails not respecting SPF


Simple, add an entry with v=spf1 mx if you want to allow your MX servers to send emails. Basically, for simple setups, the same server receive and send emails.

@ 1800 IN SPF "v=spf1 mx"


My server with the address kongroo.eu will receive the emails.

@ 10800 IN MX 50 kongroo.eu.


This part will be a bit more complicated. We have to generate a pair of public and private keys and run a daemon that will sign outgoing emails with the private key, so recipients can verify the emails signature using the public key available in the DNS. We will use opendkim, I found this very good article explaining how to use opendkim with sendmail.

Opendkim isn’t part of slackware base packages, fortunately it is available in slackbuilds, you can check my previous article explaining how to setup slackbuilds.

# groupadd -g 305 opendkim
# useradd -r -u 305 -g opendkim -d /var/run/opendkim/ -s /sbin/nologin \
    -c  "OpenDKIM Milter" opendkim
# sboinstall opendkim

We want to enable opendkim at boot, as it’s not a service from the base system, so we need to “register” it in rc.local and enable both.

Add the following to /etc/rc.d/rc.local:

if [ -x /etc/rc.d/rc.opendkim ]; then
  /etc/rc.d/rc.opendkim start

Make the scripts executable so they will be run at boot:

# chmod +x /etc/rc.d/rc.local
# chmod +x /etc/rc.d/rc.opendkim

Create the key pair:

# mkdir /etc/opendkim
# cd /etc/opendkim
# opendkim-genkey -t -s default -d kongroo.eu

Get the content of default.txt, we will use it as a content for a TXT entry in the DNS, select only the content between parenthesis without double quotes: your DNS tool (like on Gandi) may take everything without warning which would produce an invalid DKIM signature. Been there, done that.

The file should looks like:

default._domainkey      IN      TXT     ( "v=DKIM1; k=rsa; t=y; " "p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC5iBUyQ02H5sfS54hg155eQBxtMuhcwB4b896S7o97pPGZEiteby/RtCOz9VV2TOgGckz8eOEeYHnONdlnYWGv8HqVwngPWJmiU7xbyoH489ZkG397ouEJI4mBrU9ZTjULbweT2sVXpiMFCalNraKHMVjqgZWxzqoE3ETGpMNNSwIDAQAB" )

But the content I used for my entry at gandi is:

v=DKIM1; k=rsa; t=y; " "p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC5iBUyQ02H5sfS54hg155eQBxtMuhcwB4b896S7o97pPGZEiteby/RtCOz9VV2TOgGckz8eOEeYHnONdlnYWGv8HqVwngPWJmiU7xbyoH489ZkG397ouEJI4mBrU9ZTjULbweT2sVXpiMFCalNraKHMVjqgZWxzqoE3ETGpMNNSwIDAQAB

Now we need to configure opendkim to use our keys. Edit /etc/opendkim.conf to changes the following lines already there:

Domain                  kongroo.eu
KeyFile /etc/opendkim/default.private
ReportAddress           postmaster@kongroo.eu


We have to tell DMARC, this may help being accepted by big corporate mail servers.

_dmarc.kongroo.eu.   IN TXT    "v=DMARC1;p=none;pct=100;rua=mailto:postmaster@kongroo.eu;"

This will tell the recipient that we don’t give specific instruction to what to do with suspicious mails from our domain and tell postmaster@kongroo.eu about the reports. Expect daily mail from every mail server reached in the day to arrive on that address.

Install Sendmail

Unfortunately Slackware team dropped sendmail in favor to postfix in the default install, this may be a good thing but I want sendmail. Good news: sendmail is still in the extra directory.

I wanted to use citadel but it was really complicated, so I went to sendmail.


Download the two sendmail txz packages on a mirror in the “extra” directory: https://mirrors.slackware.com/slackware/slackware64-current/extra/sendmail/

Run /sbin/installpkg on both packages.


We will disable postfix.

# sh /etc/rc.d/rc.postfix stop
# chmod -x /etc/rc.d/rc.postfix

Enable sendmail and saslauthd

# chmod +x /etc/rc.d/rc.sendmail
# chmod +x /etc/rc.d/rc.saslauthd

All the configuration will be done in /usr/share/sendmail/cf/cf, we will use a default template from the package. As explained in the cf files, we need to use a template and rebuild from this directory containing all the macros.

# cp sendmail-slackware-tls-sasl.mc /usr/share/sendmail/cf/cf/config.mc

Every time we want to rebuild the configuration file, we need to apply the m4 macros to have the real configuration file.

# sh Build config.mc
# cp config.cf /etc/mail/sendmail.cf

My config.mc file looks like this (I stripped the comments):

VERSIONID(`TLS supporting setup for Slackware Linux')dnl
define(`confCACERT_PATH', `/etc/letsencrypt/live/kongroo.eu/')
define(`confCACERT', `/etc/letsencrypt/live/kongroo.eu/cert.pem')
define(`confSERVER_CERT', `/etc/letsencrypt/live/kongroo.eu/fullchain.pem')
define(`confSERVER_KEY', `/etc/letsencrypt/live/kongroo.eu/privkey.pem')
define(`confPRIVACY_FLAGS', `authwarnings,novrfy,noexpn,restrictqrun')dnl
define(`confTO_IDENT', `0')dnl
FEATURE(`mailertable',`hash -o /etc/mail/mailertable.db')dnl
FEATURE(`virtusertable',`hash -o /etc/mail/virtusertable.db')dnl
FEATURE(`access_db', `hash -T<TMPF> /etc/mail/access')dnl
FEATURE(`local_procmail',`',`procmail -t -Y -a $h -d $u')dnl
INPUT_MAIL_FILTER(`opendkim', `S=inet:8891@localhost')
define(`confAUTH_OPTIONS', `A p y')dnl
DAEMON_OPTIONS(`Port=smtp, Name=MTA')dnl
DAEMON_OPTIONS(`Port=smtps, Name=MSA-SSL, M=Esa')dnl

Create the file /etc/sasl2/Sendmail.conf with this content:


This will tell sendmail to use saslauthd for PLAIN and LOGIN connections. Any SMTP client will have to use either PLAIN or LOGIN.

If you start sendmail and saslauthd, you should be able to send e-mails with authentication.

We need to edit /etc/mail/local-host-names to tell sendmail for which domain it should accept local deliveries.

Simply add your email domain:


The mail logs are located under /var/log/maillog, every mail sent well signed with DKIM should appear under a line like this:

[time] [host] sm-mta[2520]: 0AECKet1002520: Milter (opendkim) insert (1): header: DKIM-Signature:  [whole signature]

Configure DKIM

This has been explained in a subsection of sendmail configuration. If you didn’t read this step because you don’t want to setup dkim, you missed information required for the next steps.

Install cyrus-imap

Slackware ships with dovecot in the default installation, but cyrus-imapd is available in slackbuilds.

The bad news is that the slackbuild is outdated, so here it a simple patch to apply in /usr/sbo/repo/network/cyrus-imapd. This patch also fixes a compilation issue.

diff --git a/network/cyrus-imapd/cyrus-imapd.SlackBuild b/network/cyrus-imapd/cyrus-imapd.SlackBuild
index 48e2c54e55..251ca5f207 100644
--- a/network/cyrus-imapd/cyrus-imapd.SlackBuild
+++ b/network/cyrus-imapd/cyrus-imapd.SlackBuild
@@ -23,7 +23,7 @@


@@ -107,6 +107,8 @@ CXXFLAGS="$SLKCFLAGS" \

+sed -i'' 's/gettid/_gettid/g' lib/cyrusdb_berkeley.c
 make install DESTDIR=$PKG

diff --git a/network/cyrus-imapd/cyrus-imapd.info b/network/cyrus-imapd/cyrus-imapd.info
index 99b2c68075..6ae26365dc 100644
--- a/network/cyrus-imapd/cyrus-imapd.info
+++ b/network/cyrus-imapd/cyrus-imapd.info
@@ -1,8 +1,8 @@

You can apply it by carefully copying the content in a file and use the command patch.

We can now proceed with cyrus-imapd compilation and installation.

# env DATABASE=sqlite sboinstall cyrus-imapd

As explained in the README file shown during installation, we need to do a few instructions.

# mkdir -m 750 -p /var/imap /var/spool/imap /var/sieve
# chown cyrus:cyrus /var/imap /var/spool/imap /var/sieve
# su - cyrus
# /usr/doc/cyrus-imapd-2.5.16/tools/mkimap
# logout

Add the following to /etc/rc.d/rc.local to enable cyrus-imapd at boot:

if [ -x /etc/rc.d/rc.cyrus-imapd ]; then
  /etc/rc.d/rc.cyrus-imapd start

And make the rc script executable:

# chmod +x /etc/rc.d/rc.cyrus-imapd

The official cyrus documentation is very well done and was very helpful while writing this.

The configuration file is /etc/imapd.conf:

configdirectory: /var/imap
partition-default: /var/spool/imap
sievedir: /var/sieve
admins: cyrus
sasl_pwcheck_method: saslauthd
allowplaintext: yes
tls_server_cert: /etc/letsencrypt/cyrus/fullchain.pem
tls_server_key:  /etc/letsencrypt/cyrus/privkey.pem
tls_client_ca_dir: /etc/ssl/certs

There is another file /etc/cyrusd.conf used but we don’t need to make changes in it.

We will have to copy the certificates into a separate place and allow cyrus user to read them. This will have to be done every time the certificate are renewed. Let’s add the certbot command so we can use this script as a cron.


certbot certonly --standalone -d $DOMAIN -m usernam@example
mkdir -p $DESTDIR
install -o cyrus -g cyrus -m 400 $LIVEDIR/fullchain.pem $DESTDIR
install -o cyrus -g cyrus -m 400 $LIVEDIR/privkey.pem $DESTDIR
/etc/rc.d/rc.sendmail restart
/etc/rc.d/rc.cyrus-imapd restart

Add a crontab entry to run this script once a day, using crontab -e to change root crontab.

0 5 * * * sh /root/renew_certs.sh

Starting the mail server

We prepared the mail server to be working on reboot, but the services aren’t started yet.

# /etc/rc.d/rc.saslauthd start
# /etc/rc.d/rc.sendmail start
# /etc/rc.d/rc.cyrus-imapd start
# /etc/rc.d/rc.opendkim start

Adding a new user

Add a new user to your system.

# useradd $username
# passwd $username

For some reasons the user mailboxes must be initialized. The same password must be typed twice (or passed as parameter using -w $password).

# USER=foobar
# DOMAIN=kongroo.eu
# echo "cm INBOX" | rlwrap cyradm -u $USER $DOMAIN
IMAP Password:

Voila! The user should be able to connect using IMAP and receive emails.

Check your email setup

You can use the web service Mail tester by sending an email. You could copy/paste a real email to avoid having a bad mark due to spam recognition (which happens if you send a mail with a few words). The bad spam core isn’t relevant anyway as long as it’s due to the content of your email.


I had real fun writing this article, digging hard in Slackware and playing with unusual programs like sendmail and cyrus-imapd. I hope you will enjoy too as much as I enjoyed writing it!

If you find mistakes or bad configuration settings, please contact me so, I will be happy to discuss about the change and fix this how-to.

Nota Bene: Slackbuilds aren’t mean to be used on the current version, but really on the last release. There is a github repository carrying the -current changes on a github repository https://github.com/Ponce/slackbuilds/.

prose - Blogging with email

Written by Solène, on 11 June 2020.
Tags: #blog #email #blog #plaintext

Comments on Mastodon

The software developer prx, his website is available at https://ybad.name/ (en/fr), released a new software called prose to publish a blog by sending emails.

I really like this idea, while this doesn’t suit my needs at all, I wanted to write about it.

The code can be downloaded from this address https://dev.ybad.name/prose/ .

I will briefly introduce how it works but the README file is well explaining, prose must be started from the mail server, upon email receival in /etc/mail/aliases the email will be piped into prose which will produce the html output.

On the security side, prose doesn’t use any external command and on OpenBSD it will use unveil and pledge features to reduce privileges of prose, unveil will restrict the process file system accesses outside of the html output directory.

I would also congrats prx who demonstrates again that writing good software isn’t exclusive to IT professionnal.

Extract files from winmail.dat

Written by Solène, on 02 May 2018.
Tags: #unix #email

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If you ever receive a mail with an attachment named “winmail.dat” then may be disappointed. It is a special format used by Microsoft Exchange, it contains the files attached to the mail and need some software to extract them.

Hopefully, there is a little and effecient utility named “tnef” to extract the files.

Install it: pkg_add tnef

List files: tnef -t winmail.dat

Extract files: tnef winmail.dat

That’s all !

Using emacs to manage mails with mu4e

Written by Solène, on 15 June 2017.
Tags: #emacs #email

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In this article we will see how to fetch, read and manage your emails from Emacs using mu4e. The process is the following: mbsync command (while mbsync is the command name, the software name is isync) create a mirror of an imap account into a Maildir format on your filesystem. mu from mu4e will create a database from the Maildir directory using xapian library (full text search database), then mu4e (mu for emacs) is the GUI which queries xapian database to manipulates your mails.

Mu4e handles with dynamic bookmarks, so you can have some predefined filters instead of having classic folders. You can also do a query and reduce the results with successives queries.

You may have heard about using notmuch with emacs to manage mails, mu4e and notmuch doesn’t do the same job. While notmuch is a nice tool to find messages from queries and create filters, it operates as a read-only tool and can’t do anything with your mail. mu4e let you write mail, move, delete, flag etc… AND still allow to make complex queries.

I wrote this article to allow people to try mu4e quickly, you may want to read both isync and mu4e manual to have a better configuration suiting your needs.


On OpenBSD you need to install 2 packages:

# pkg_add mu4 isync

isync configuration

We need to configure isync to connect to the IMAP server:

Edit the file ~/.mbsyncrc, there is a trick to not have the password in clear text in the configuration file, see isync configuration manual for this:

iMAPAccount my_imap
Host my_host_domain.info
User imap_user
Pass my_pass_in_clear_text

IMAPStore my_imap-remote
Account my_imap

MailDirStore my_imap-local
Path ~/Maildir/my_imap/
Inbox ~/Maildir/my_imap/Inbox
SubFolders Legacy

channel my_imap
Master :my_imap-remote:
Slave :my_imap-local:
Patterns *
Create Slave
Expunge Both

mu4e / emacs configuration

We need to configure mu4e in order to tell where to find the mail folder. Add this to your ~/.emacs file.

(require 'mu4e)
(setq mu4e-maildir "~/Maildir/my_imap/"
      mu4e-sent-folder "/Sent Messages/"
      mu4e-trash-folder "/Trash"
      mu4e-drafts-folder "/Drafts")

First start

A few commands are needed in order to make everything works. We need to create the base folder as mbsync command won’t do the job for some reason, and we need mu to index the mails the first time.

mbsync can takes a moment because it will download ALL your mails.

$ mkdir -p ~/Maildir/my_imap
$ mbsync -aC
$ mu init --maildir=~/Maildir/my_imap
$ mu index

How to use mu4e

start emacs, run M-x mu4e RET and enjoy, the documentation of mu4e is well done. Press “U” at mu4e screen to synchronize with imap server.

A query for mu4e looks like this:

list:misc.openbsd.org flag:unread avahi

This query will search mails having list header “misc.openbsd.org” and which are unread and which contains “avahi” pattern.

date:20140101..20150215 urgent

This one will looks for mails within date range of 1st january 2014 to 15th february 2015 containing word “urgent”.

Additional notes

The current setup doesn’t handle sending mails, I’ll write another article about this. This requires configuring a smtp authentification and an identify for mu4e.

Also, you may need to tweak mbsync configuration or mu4e configuration, some settings must be changed depending on the imap server, this is particuliarly important for deleted mails.

Port of the week: rss2email

Written by Solène, on 24 January 2017.
Tags: #portoftheweek #unix #email

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This is the kind of Port of the week I like. This is a software I just discovered and fall in love to. The tool r2e which is the port mail/rss2email on OpenBSD is a small python utility that solves a problem: how to deal with RSS feeds?

Until last week, I was using a “web app” named selfoss which was aggregating my RSS feeds and displaying it on a web page, I was able to filter by read/unread/marked and also filter by source. It is a good tool that does the job well but I wanted something that doesn’t rely on a web browser. Here comes r2e !

This simple software will send you a mail for each new entry in your RSS feeds. It’s really easy to configure and set-up. Just look at how I configured mine:

$ r2e new my-address+rss@my-domain.com
$ r2e add "http://undeadly.org/cgi?action=rss"
$ r2e add "https://dataswamp.org/~solene/rss.xml"
$ r2e add "https://www.dragonflydigest.com/feed"
$ r2e add "http://phoronix.com/rss.php"

Add this in your crontab to check new RSS items every 10 minutes:

*/10 * * * * /usr/local/bin/r2e run

Add a rule for my-address+rss to store mails in a separate folder, and you’re done !

NOTE: you can use r2e run –no-send for the first time, it will create the database and won’t send you mails for current items in feeds.

Dovecot: folder appears empty

Written by Solène, on 23 January 2017.
Tags: #email

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Today I encountered an unknown issue to me with my Imap server dovecot. In roundcube mail web client, my Inbox folder appeared empty after being reading a mail. My Android mail client K9-Mail was displaying “IOException:readStringUnti….” when trying to synchronize this folder.

I solved it easily by connecting to my server with SSH, cd-ing into the maildir directory and in the Inbox folder, renamed dovecot.index.log to dovecot.index.log.bak (you can remove it if it fix the problem).

And now, mails are back. This is the very first time I have a problem of this kind with dovecot…

Convert mailbox to maildir with dovecot

Written by Solène, on 17 January 2017.
Tags: #unix #email

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I have been using mbox format for a few years on my personal mail server. For those who don’t know what mbox is, it consists of only one file per folder you have on your mail client, each file containing all the mails of the corresponding folder. It’s extremely ineficient when you backup the mail directory because it must copy everything each time. Also, it reduces the system cache possibility of the server because if you have folders with lots of mails with attachments, it may not be cached.

Instead, I switched to maildir, which is a format where every mail is a regular file on the file system. This takes a lot of inodes but at least, it’s easier to backup or to deal with it for analysis.

Here how to switch from mbox to maildir with a dovecot tool.

# dsync -u solene mirror mbox:~/mail/:INBOX=~/mail/inbox

That’s all ! In this case, my mbox folder was ~/mail/ and my INBOX file was ~/mail/inbox. It tooks me some time to find where my INBOX really was, at first I tried a few thing that didn’t work and tried a perl convert tool named mb2md.pl which has been able to extract some stuff but a lot of mails were broken. So I have been going back getting dsync working.

If you want to migrate, the whole process looks like:

# service smtpd stop

modify dovecot/conf.d/10-mail.conf, replace the first line
mail_location = mbox:~/mail:INBOX=/var/mail/%u   # BEFORE
mail_location = maildir:~/maildir                # AFTER

# service dovecot restart
# dsync -u solene mirror mbox:~/mail/:INBOX=~/mail/inbox
# service smtpd start

How to send html signature in mu4e

Written by Solène, on 07 June 2016.
Tags: #email #emacs

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I switched to mu4e to manage my mails at work, and also to send mails. But in our corporation we all have a signature that include our logo and some hypertext links, so I couldn’t just insert my signature and be done with that. There is a simple way to deal with this problem, I fetched the html part of my signature (which include an image in base64) and pasted it into my emacs config file this way.

(setq mu4e-compose-signature 
  "<#part type=text/html><html><body><p>Hello ! I am the html signature which can contains anything in html !</p></body></html><#/part>" )

I pasted my signature instead of the hello world text of course, but you only have to use the part tag and you are done ! The rest of your mails will be plain text, except this part.

Mbsync and imap login problem

Written by Solène, on 17 May 2016.
Tags: #solved #email

Comments on Mastodon

I have not found any answer about this so I share my fixed. I wanted to use mbsync with one IMAP server and encountered the following error.

IMAP command 'AUTHENTICATE DIGEST-MD5' returned an error: NO Authentication failed

A fix is to add the following to your ~/.mbsyncrc IMAPAccount declaration.

AuthMechs LOGIN

Using LOGIN instead of DIGEST-MD5 is still secure if you have an encrypted connection (IMAPS or STARTTLS). The login will be given plaintext inside the connection.

My mutt cheat sheet

Written by Solène, on 03 May 2016.
Tags: #cheatsheet #mutt #email

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I am learning mutt and I am lost. If you are like me, you may like the following cheat sheet!

I am using it through imap, it may be different with local mailbox.

Case is important !

  • Change folder : Y
  • Filter the display : l (for limit) and then a filter like this
  • ~d <2w : ~d for date and <2w for “less than 2 weeks” no space in <2w !
  • ~b “hello mate” : ~b is for body and the string is something to find in the body
  • ~f somebody@zxy.abc : ~f for from and you can make an expression
  • ~s “Urgent” : ~s stands for subject and use a pattern
  • Delete messages with filter : D with a filter, if you used limit before it will propose by default the filter of limit
  • Delete a message : d (it will be marked as Deleted)

Deleted messages will be removed when you change the folder or if you exit. Pressing $ can do it manually.