Redhat 7 Mail Configuration for Sending ( Relay ) Mail

What is Mailx?

Postfix is an Mail Server (MTA) — a Message Transfer Agent.

Mailx is an Mail Client (MUA) — a Mail User Agent. Mailx used for send and recieve emails from Mail Server (Postfix)

How does it work? 

mail -> sendmail -> local MTA -> recipient MTA [Inbox]

# Check Postfix and Mailx is Installed and Running
yum install -y postfix
yum install -y mailx
systemctl enable postfix
systemctl restart postfix
# Check the non-default configuration 
postconf -n
# Set relayhost to postfix configuration
postconf -e 'relayhost = 192.168.1.1'
# Check the syntax
postfix check
# Open the firewall if you want to receive emails from outside
firewall-cmd --permanent --add-service=smtp
firewall-cmd --reload
# Test
echo "This is a test." | mail -s "Test" me@example.com
# Troubleshooting
netstat -ltnp | grep 25
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      13303/master
tcp6       0      0 ::1:25                  :::*                    LISTEN      13303/master

#   Usage Options
#      -v = Verbosity
#      -s = Specifies the subject.
#      -r = Email sent from.
#      -c = CC
#      -b = BCC
#      -S = Specifies the smtp server.
#      -a = Attachment

#   Some Examples
echo "This is test mail" |  mail -r "FROM" -s "SUBJECT" mahmut.deniz@domain.com.tr

mailx -s "SUBJECT" mahmut.deniz@domain.com.tr < message.txt

more message.txt | mailx -s deneme mahmut.deniz@domain.com.tr,ege.deniz@yok.gov.tr

mailx -a file.txt -s "Subject" mahmut.deniz@domain.com.tr < /dev/null