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Mail Part 1 Setup Smtp Opensmtpd

26 Jul 2015

This is mostly my personal mail server documentation a bit polished in three blog posts.

DNS setup

Set a MX record to a subdomain like mail.domain.tdl and then the mail.domain.tdl points to your IP. Don't forget to increase the TTL of this records if everything works. Why? I set my TTL to 259200 sec, which are 3 days

Make sure your reverse DNS match the hostname of your mail server!

And you should probably set the Sender Policy Framework

doamin.tdl.                 IN   TXT    "v=spf1 mx mx:domain.tdl -all"

Create users

Now we need a user, replace $USERNAME with the account name. If your email address should be hi@domain.tdl your account name is hi.

pw user add $USERNAME -m -s /sbin/nologin -c "mail user ($USERNAME)" # create user account
passwd $USERNAME                                                     # change password

mkdir /home/$USERNAME/mbox                                           # create mail directory
chown -R $USERNAME:$USERNAME /home/$USERNAME/mbox                    # own the directory to the right user

If you need to create a few accounts maybe use this script, where you can just run this script with the user name as parameter.

Install OpenSMTPD

Before we can install OpenSMTPD we need to stop and remove sendmail. So first we stop it with:

service sendmail stop

Then we can edit /etc/rc.conf and add these lines, to make sure sendmail is not started automaticly after a reboot.

sendmail_enable="NONE"

Now we can install OpenSMTPD which is really really easy, it's just:

pkg install opensmtpd

and add to /etc/rc.conf

smtpd_enable="YES"

and your done. Well almost we need to create the SSL certificates and configure the OpenSMTPD.

Create your SSL certs

As the first step we symlink the certificate root to the global certificate root location. If it's not alreay done.

ln -s /usr/local/etc/ssl/cert.pem /etc/ssl/cert.pem

At this point we can create our certificates.

openssl genrsa -out /usr/local/openssl/private/mail.domain.tdl.key 4096
openssl req -new -x509 -key /usr/local/openssl/private/mail.domain.tdl.key -out /usr/local/openssl/certs/mail.domain.tdl.crt -days 1440

Country Name (2 letter code) [AU]: NL
State or Province Name (full name) [Some-State]:Amsterdam         
Locality Name (eg, city) []:Amsterdam
Organization Name (eg, company) [Internet Widgits Pty Ltd]:l33tsource Ltd
Organizational Unit Name (eg, section) []:
Common Name (e.g. server FQDN or YOUR name) []:mail.domain.tdl
Email Address []:admin@domain.tdl

By default these key and certificate should only be accessible to the root user. So we fix that with chmod.

chmod 500 /usr/local/openssl/private/mail.domain.tdl.key
chmod 500 /usr/local/openssl/certs/mail.domain.tdl.crt

OpenSMTPD configuration

With the SSL certificate in place we can edit the smtpd config (/usr/local/etc/mail/smtpd.conf).

pki mail.domain.tdl key "/usr/local/openssl/private/mail.domain.tdl.key"
pki mail.domain.tdl certificate "/usr/local/openssl/certs/mail.domain.tdl.crt"

listen on lo1 port 25 hostname mail.domain.tdl tls pki mail.domain.tdl
listen on lo1 port 587 hostname mail.domain.tdl tls-require pki mail.domain.tdl auth mask-source

table aliases file:/etc/mail/aliases

accept from any for domain "domain.tdl" alias <aliases> deliver to maildir "~/mbox"
accept from local for any relay

This is it. Really simple and short. What this does is listen on port 25 and 587 on the lo1 interface (this should obviously match your interface) and accept encrypted connections. The key and certificate location are configured with the pki keyword. And the messages are delivered to the home directory of the user in a folder called mbox.

Now we can start the smtpd service and test it with telnet.

telnet servername 25
	EHLO mail.domain.tdl 
	MAIL FROM:<FROM@domain.tdl> 
	RCPT TO:<TO@domain.tdl> 
	DATA 
	Subject: Testmessage 
	(blank line) 
	This is a test.
	(blank line) 
	. 
	QUIT

If it's says something like 250 2.0.0: 5x549x2a Message accepted for delivery, congratulation your SMTP works.

This is the first part of a three part series:

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