refactor: kb article on the mail util

knowledge base/mail.md

@@ -0,0 +1,63 @@
+# Mail
+
+1. [TL;DR](#tldr)
+1. [Further readings](#further-readings)
+   1. [Sources](#sources)
+
+## TL;DR
+
+```sh
+# Just test the presence for new emails.
+# Exit status '0' means there are, '1' there is none.
+mail -e
+
+# Read all unread emails at once.
+cat '/var/mail/username'
+
+# Read automatically saved messages.
+cat "$HOME/mbox"
+
+# Send emails.
+mail -s 'Subject' 'recipient@mail.server'
+echo '' | mail -a 'attachment.file' -s 'Subject' 'recipient@mail.server'
+
+# Send larger files.
+cat 'file.txt' | mail -s 'Subject' 'recipient@mail.server'
+
+# Make "email-safe" the contents of a file before sending it.
+uuencode 'file.txt' | mail -s 'Subject' 'recipient@mail.server'
+
+# Delete all emails at once.
+echo -n > '/var/mail/username'
+sudo rm '/var/mail/username'
+```
+
+| Command                                                       | Description                                          |
+| ------------------------------------------------------------- | ---------------------------------------------------- |
+| `?`                                                           | View the help                                        |
+| `p`, `print`<br/>`p 3`<br/>`p 3 6`<br/>`p 3-10`<br/>`p *`     | Print all messages in the list to the default output |
+| `t`, `type`                                                   | Synonym for `p`                                      |
+| `mo`, `more`<br/>`mo 3`<br/>`mo 3 6`<br/>`mo 3-10`<br/>`mo *` | Print all messages in the list to the default pager  |
+| `n`, `next`<br/>`n 3`<br/>`n 3 6`<br/>`n 3-10`<br/>`n *`      | Print the next message in the list                   |
+| `d`, `delete`<br/>`d 3`<br/>`d 3 6`<br/>`d 3-10`<br/>`d *`    | Mark all messages in the list as deleted             |
+| `q`, `quit`                                                   | Quit saving unresolved messages under `~/mbox`       |
+| `x`, `ex`, `exit`                                             | Quit **without** making changes to the mailbox       |
+
+## Further readings
+
+### Sources
+
+- [`man` page][man page]
+
+<!--
+  References
+  -->
+
+<!-- In-article sections -->
+<!-- Knowledge base -->
+<!-- Files -->
+<!-- Upstream -->
+<!-- Others -->
+[linux mail command examples]: https://www.binarytides.com/linux-mail-command-examples/
+[man page]: https://linux.die.net/man/1/mail
+[uuencode]: https://linux.101hacks.com/unix/uuencode/

knowledge base/send an email from cli.md

@@ -1,32 +1,10 @@
 # Send an email from CLI
 
-## Table of contents <!-- omit in toc -->
+For Unix-like systems, see [`mail`][mail].
-
-1. [TL;DR](#tldr)
-1. [Further readings](#further-readings)
-
-## TL;DR
-
-```sh
-mail -s "Subject" recipient@mail.server
-echo "" | mail -a attachment.file -s "Subject" recipient@mail.server
-
-# send larger files
-cat file.txt | mail -s "Subject" recipient@mail.server
-
-# make "email-safe" the contents of a file
-uuencode file.txt | mail -s "Subject" recipient@mail.server
-```
-
-## Further readings
-
-- [linux mail command examples]
-- [uuencode]
 
 <!--
   References
   -->
 
-<!-- Others -->
+<!-- Knowledge base -->
-[linux mail command examples]: https://www.binarytides.com/linux-mail-command-examples/
+[mail]: mail.md
-[uuencode]: https://linux.101hacks.com/unix/uuencode/