Add 'ssmtp_conf-sample/README.md'

ssmtp_conf-sample/README.md

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+## sSMTP system pre-configuration
+
+Once you have installed sSMTP on your Linux system, make sure the following applies. Run the configuration commands as root or with `sudo` prefix.
+
+----------
+
+Symbolic link from `/usr/bin/ssmtp` to `/usr/bin/sendmail`:
+
+```
+ln -s /usr/bin/ssmtp /usr/bin/sendmail
+```
+
+```
+Test:
+
+    > stat -c "%A %a %U:%G %N" /usr/bin/sendmail
+
+        lrwxrwxrwx 777 root:root /usr/bin/sendmail -> ssmtp
+```
+
+----------
+
+User & group mail exists, directory /`var/spool/mail` exists:
+
+```
+mkdir -p /var/spool/mail
+chmod 1777 /var/spool/mail
+
+groupadd -g 12 mail
+useradd -r -d /var/spool/mail -s /sbin/nologin -u 12 -g 12 mail
+```
+
+```
+Test:
+
+-----
+    > sudo stat -c "%A %a %U:%G %n" /var/spool/mail
+
+        drwxrwxrwt 1777 root:root /var/spool/mail
+
+-----
+    > grep mail /etc/passwd
+
+        mail:x:12:12::/var/spool/mail:/sbin/nologin
+
+-----
+    > grep mail /etc/group
+
+        mail:x:12:
+```
+
+## sSMTP configuration files
+
+Once you have sSMTP installed on your Linux system, insert [ssmtp.conf](ssmtp.conf), [revaliases](revaliases) and [wanchecker.sh](wanchecker.sh) into `/etc/ssmtp/` folder. These files should have following permissions:
+
+```
+> stat -c "%A %a %U:%G %n" /etc/ssmtp/*
+
+-rw-r----- 640 root:mail /etc/ssmtp/revaliases
+-rw-r----- 640 root:mail /etc/ssmtp/ssmtp.conf
+-rwxr-x--- 750 root:mail /etc/ssmtp/wanchecker.sh
+
+```
+
+where group `mail` refers to Arch Linux mail group, preinstalled with `filesystem` package.