====== Configure A System To Forward All Email To A Central Mail Server ======

**General Information**

Configuring postfix.

On the exam, you will be provided all the information of an already configured central SMTP server.

**You will be expected to configure a null client only**. (server that forwards mail but does not receive any)

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====== Lab Setup ======

The following virtual machines will be used:
  * server1.example.com (192.168.1.150) -> Configure SMTP null client (**on the exam**)
  * server2.example.com (192.168.1.151) -> Configure central mail server for client testing (**NOT on the exam**)

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====== Null Client Setup ======

**THIS IS ON THE EXAM**: A mail null client forwards local email. It does not receive any mail from network sources.

**From server1**.

\\
Install required package
<code bash>
yum install postfix
</code>

\\
Enable and start the postfix service
<code bash>
systemctl enable postfix
systemctl start postfix
</code>

\\
Configure postfix parameters
  * Option A: Use postconf (faster if you have an idea what parameters you need to configure)<code bash># check a setting
postconf relayhost

# check all settings
postconf | grep <keyword>

# configure - important
postconf -e 'relayhost = [192.168.1.151]'

# configure - probably already defaults (or set to localhost)
postconf -e 'inet_interfaces = loopback-only'
postconf -e 'mydestination ='
postconf -e 'mydomain = example.com'
</code>
  * Option B: Edit the main configuration<code bash>vim /etc/postfix/main.cf

# Relayhost to forward mail to
relayhost = [192.168.1.151]

# Forward from loopback interfaces
inet_interfaces = loopback-only

# Configure destination as blank, because we aren't delivering mail locally (only forwarding outgoing)
mydestination = 

# Configure domain
mydomain = example.com
</code>


\\
Check postfix syntax
<code bash>
postfix check
</code>

\\
Restart the service
<code bash>
systemctl restart postfix
</code>

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====== Postfix Central Mail Server ======

**THIS IS NOT ON THE EXAM**: This section setups up a mail server to receive mail in order to test the null client configured previously.

**From server2**

\\
Install postfix
<code bash>
yum install postfix
</code>

\\
Enable and start postfix
<code bash>
systemctl enable postfix
systemctl start postfix
</code>

\\
Open the firewall to receive SMTP
<code bash>
firewall-cmd --permanent --add-service=smtp
firewall-cmd --reload
</code>

\\
Edit the main configuration file
<code bash>
#-- vim directly
vim /etc/postfix/main.cf

# listening interfaces
inet_interfaces = all

# Accept mail for these domains
mydestination = example.com, server2.example.com, server2

#-- postconf method
 
# check settings
postconf | grep inet_
postconf | grep mydestination
 
# configure
postconf -e 'inet_interfaces = all'
postconf -e 'mydestination = example.com, server2.example.com, server2'
</code>

\\
Check postfix syntax
<code bash>
postfix check
</code>

\\
Restart the service
<code bash>
systemctl restart postfix
</code>

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====== Null Client Testing ======

**From server1**

Install a mail client (if not already installed)
<code bash>
yum install mailx
</code>

\\
Send a test message
<code bash>
echo "Did it work?" | mail -s "This is a postfix forward test" root@server2.example.com
</code>

\\
Watch the mail log file for status messages
<code bash>
tail -f /var/log/maillog
</code>

\\
**From server2**

On the postfix relayhost, check root's mail
<code bash>
mail
</code>

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====== Troubleshooting ======

On the sending client, to view the mail queue
<code bash>
postqueue -p
</code>

\\
Flush the sending mail queue after fixing a problem to get rid of stuck messages
<code bash>
postqueue -f
</code>

\\
If a message is stuck and won't flush, it can be removed
<code bash>
postsuper -d <queue_id>
</code>
  * Instead of a single queue_id, you can specify the keyword 'ALL'

\\
On the receiving server, check the maillog for reasons a message did not deliver
<code bash>
tail /var/log/maillog
</code>

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