DokuWiki » Infrastructure » Operating System » CentOS 9

h1. Setting up Postfix to send mails via external mail-account

h2. Preliminary note

See also:

* https://www.zulius.com/how-to/set-up-postfix-with-a-remote-smtp-relay-host/

* http://rs20.mine.nu/w/2011/07/gmail-as-relay-host-in-postfix/

A typical email scenario: you're a developer, and you've got a development Linux box at home. You need to be able to send emails from your code or cron jobs, but you're too lazy to set up a full fledged email server on your LAN. Or you just want to use an email account provided by Google Apps, Yahoo, your ISP or in our case a iRedMail-installation.

h2. Install postfix

Should be preinstalled, as it is the default mail-handler with CentOS

<pre><code class="bash">

dnf install postfix cyrus-sasl cyrus-sasl-gssapi cyrus-sasl-plain

</code></pre>

h2. configure postfix

<pre><code class="bash">

vim /etc/postfix/main.cf

</code></pre>

<pre>

# line ~118...

myorigin = example.com

# Set this to your email provider's smtp server.

# A lot of ISP's (ie. Cox) block the default port 25

# for home users to prevent spamming.  So we'll use port 587

# line ~339...

relayhost = mail.example.com:587

# add at end of file...

smtpd_sasl_auth_enable = yes

smtpd_sasl_path = smtpd

smtp_use_tls = yes

smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd

smtp_sasl_type = cyrus

smtp_sasl_auth_enable = yes

# optional: necessary if email provider uses load balancing and

# forwards emails to another smtp server

# for delivery (ie: smtp.yahoo.com --> smtp.phx.1.yahoo.com)

smtp_cname_overrides_servername = no

# optional: necessary if email provider

# requires passwords sent in clear text

smtp_sasl_security_options = noanonymous

canonical_maps = hash:/etc/postfix/canonical

</pre>

additionally we need to know the server and email-address as well as the password to use

<pre><code class="bash">

vim /etc/postfix/sasl_passwd

</code></pre>

<pre>

mail.example.com:587     mailadr@example.com:password

</pre> 

The above server hostname and port must exactly match the value for "relayhost" in /etc/postfix/main.cf.

Generate a postfix lookup table from the previous file

<pre><code class="bash">

postmap hash:/etc/postfix/sasl_passwd

</code></pre>

Test the lookup table, if all is good then the following will return the specified username:password

<pre><code class="bash">

postmap -q mail.example.com:587 /etc/postfix/sasl_passwd

</code></pre>

next is to bind the local username to the email-address. You may also have a look into @/etc/aliases@ and check who's mail are sent to whom.

<pre><code class="bash">

vim /etc/postfix/canonical

</code></pre>

<pre>

root     mailadr@example.com

</pre> 

The above email-address must exactly match the email-address in sasl_passwd.

Generate a postfix lookup table from the previous file

<pre><code class="bash">

postmap hash:/etc/postfix/canonical

</code></pre>

Make sure that sasl_passwd and sasl_passwd.db files are readable/writeable only by root

<pre><code class="bash">

chmod 600 /etc/postfix/sasl_passwd

chmod 600 /etc/postfix/sasl_passwd.db

</code></pre>

Add postfix to be started at boot

<pre><code class="bash">

systemctl enable postfix

</code></pre>

h2. Test postfix

Fire up Postfix

<pre><code class="bash">

systemctl start postfix

</code></pre>

Test it out using sendmail alias from the command prompt

<pre><code class="bash">

sendmail email@any.com

Postfix is good to go.

.

</code></pre>