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:
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> sudo stat -c "%A %a %U:%G %n" /var/spool/mail
drwxrwxrwt 1777 root:root /var/spool/mail
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> grep mail /etc/passwd
mail:x:12:12::/var/spool/mail:/sbin/nologin
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> grep mail /etc/group
mail:x:12:
Once you have sSMTP installed on your Linux system, insert ssmtp.conf, revaliases and 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.