Your own Mailing List

Quick why and what

If you're like me, your email inbox is like a second home. Information about friends, events, and all sorts of things come filtering through. A lot of the time you might have a designated group of friends whom you share a lot of links with. If you use gmail or any decent webmail client you're likely familiar with the concept of lists.

Within your inbox, you can add a list of users into a group that you can then email easily. Within gmail, these groups expand out into the numerous users you want to talk to, you write an email, and off it goes. Welcome to the information age. However, sometimes people forget to hit 'reply-all', or they want to share information too, but they only sent it to you. So you forward it out to everyone on your group and then proceed to enjoy the thought catalog coming your way.

But if you're like me, you'd prefer if everyone could share a group. So that everyone can email the one address and instantly everyone who cares to be on the mailing list is enjoying it. In this blog post, I'm going to show you how to set up your own mailing list.

What you'll need

Postfix? Sendmail? What do I use?!

When setting up an SMTP typically one uses sendmail or postfix and if you're lucky, one might even come preinstalled on your distro. For me, I wanted a mail server that could use a whitelist and blacklist without too much of a hassle. Since sendmail doesn't really support that, I installed postfix instead since it does.

Install postfix

Installing postfix is easy, on debian just use apt: 

sudo su
aptitude install postfix

It will ask you a few questions during the configuration, one of the important ones to note is when you're setting up your FQDN (Fully Qualified Domain Name). It should be set to the output of hostname --fqdn on your machine. Also, when asked which configuration option you'd like, set it to "Internet Site" as you'll be wanting to recieve and sendmail from your machine to facilate the mailing list.

Configuring postfix

Next, you need to configure. This can be done by checking out two files:

  1. /etc/postfix/main.cf

  2. /etc/postfix/master.cf

main.cf is the file you'll want to spend some time on. If you want to understand the file, I suggest reading the documentation. It's rather helpful and answers a lot of questions you might have right off the bat. The configuration that I changed was as follows: 

myhostname = your.domain.here.com
mydestination = your.domain.here.com, $myhostname, localhost.info, localhost, mail.your.domain.here.com, mail.$hostname
mynetworks_style = host
notify_classes = bounce, resource, software
smtpd_recipient_restrictions = check_client_access hash:/etc/postfix/client_checks, check_sender_access hash:/etc/postfix/sender_checks, reject_unauth_destination

The last line of the configuration is to setup a whitelist. Note that the linked blogpost does not include the reject_unauth_destination, this was neccesary because otherwise you're going to get a lot of errors like this in your log: 

postfix/smtpd[1435]: fatal: parameter "smtpd_recipient_restrictions": specify at least one working instance of: check_relay_domains, reject_unauth_destination, reject, defer or defer_if_permit

Taking note of /etc/syslog.conf you'll want to be sure where your mail server is logging to. Then the handy dandy: tail -n 20 /var/log/mail.* can help you figure out what's going wrong if anything does.

Setting up the mailing list

First, make a username for the alias you'll use. Let's pretend you're setting up a mailing list for your family to share vacation pictures and have decided that your mailing list will be called "vacations" (creative I know). 

useradd vacations
passwd vacations #enter a password

vi /etc/aliases #if you're using vim, use nano if you'd like, or emacs or whatever

Once the aliases file is open simply add in a section like this near the bottom: 

#/etc/aliases

#... bunch of stuff

vacations:
  mom@domain.com
  dad@domain.com
  brother@domain.com
  sister@domain.com
  #etc etc list all the email addresses you want in here
  #Note, if you're using a whitelist then make sure they're included

Then run the command to refresh your aliases: 

newaliases
postalias /etc/aliases #important!
/etc/init.d/postfix reload

If you're using a whitelist make sure to create the databases for your mail server by running the following: 

#You'll need to make the *_checks files first obviously, see the link above
postmap /etc/postfix/client_checks
postmap /etc/postfix/sender_checks
/etc/init.d/postfix reload

Once this is all setup it's time to setup your DNS records. Go into your providers configuration and look for MX records. For some providers they may already have FAQ's or tutorials on setting up your mailserver to relay to theirs. But a quick and dirty approach is to simply edit the MX record to point directly to your server's IP address.

Next, if you're running a firewall you'll want to punch a hole in it for your mail server to talk through. If you're using ufw all you need to do is run the command: ufw allow smtp and you should end up with a status like this: 

$ufw status
Status: active

To                         Action      From
--                         ------      ----
22                         ALLOW       Anywhere
80                         ALLOW       Anywhere
443/tcp                    ALLOW       Anywhere
25/tcp                     ALLOW       Anywhere
22                         ALLOW       Anywhere (v6)
80                         ALLOW       Anywhere (v6)
443/tcp                    ALLOW       Anywhere (v6)
25/tcp                     ALLOW       Anywhere (v6)

Once this is done, you'll want to test the mailing list. Go back to your aliases file and comment out (use a #) everyone but you and a test email and write an email to your new alias: "vacations@domain.com". Before you send it, tail the log on your server with: tail -f /var/log/mail.info

If you don't see something like 

postfix/smtpd[1520]: connect from unknown[x.x.x.x]
postfix/smtpd[1520]: warning: support for restriction "check_relay_domains" will be removed from Postfix; use "reject_unauth_destination" instead
postfix/smtpd[1520]: 640932615C2: client=unknown[x.x.x.x]
postfix/cleanup[1524]: 640932615C2: message-id=<someidofthemessagesender@mail.gmail.com>
postfix/qmgr[1460]: 640932615C2: from=<testuser@yourhost.com>, size=3422, nrcpt=1 (queue active)
postfix/cleanup[1524]: 7EDEB2615C3: message-id=<someidofthemessagesender@mail.gmail.com>
postfix/qmgr[1460]: 7EDEB2615C3: from=<testuser@yourhost.com>, size=3568, nrcpt=2 (queue active)
postfix/local[1525]: 640932615C2: to=<vacations@yourdomain.com>, relay=local, delay=0.12, delays=0.11/0.01/0/0, dsn=2.0.0, status=sent (forwarded as 7EDEB2615C3)
postfix/qmgr[1460]: 640932615C2: removed
postfix/smtpd[1520]: disconnect from unknown[x.x.x.x]
postfix/smtp[1526]: 7EDEB2615C3: to=<test@cock.li>, orig_to=<vacations@yourdomain.com>, relay=mail.cock.li[x.x.x.x]:25, delay=0.15, delays=0/0.01/0.07/0.07, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as 97A5B26116B)
postfix/smtp[1527]: 7EDEB2615C3: to=<youremail@domain.com>, orig_to=<vacations@yourdomain.com>, relay=gmail-smtp-in.l.google.com[x.x.x.x]:25, delay=0.43, delays=0/0.02/0.06/0.35, dsn=2.0.0, status=sent (250 2.0.0 OK 1418057717 n77si43908260q1d.64 - gsmtp)
postfix/qmgr[1460]: 7EDEB2615C3: removed

then you'll want to check your .err,.info, and .warn logs, a quick way to do so is to run tail /var/log/mail.* and look at the timestamps to determine where the mail you sent was.

Once you've got test emails working you'll want to uncomment the real email addresses you'd like to use and remove the test ones. After this, it's happy emailing and your friends and you should be able to share information with everyone at once with a single address.

A few gotchas

Mail server's can suck to debug sometimes, this is mainly because they're out in the wild wild west (www) and lots can go wrong. Here's a few issues you might run into and their fixes:

My email keeps getting sent back to me!

If you're getting emails with something like: "Relay access denied" then you need to take a look at your DNS settings and make sure they're pointing to your server. If they are, try asking your DNS provider about MX records and the error.

I send the email, it hits a test address, but doesn't show up in my own inbox on gmail

In this case, you might be hitting this problem with postfix, in which case there's not much to be done, but trust that your email is being delivered. On the bright side, you'll see the email if someone replies back to your list. So all is well.

Problems installing postfix with apt-get?

If you're using apt-get and have funny repositories you might run into some weird glitches where the the machine yells about not being able to do anything, just try out aptitude and say no to the first option then agree to one that downgrades incompatible versions of other software.

aliases.db is older than source file?

postfix/smtpd[1307]: warning: database /etc/aliases.db is older than source file /etc/aliases

If you get the above error, just run newaliases and you should be all set

No client.db or sender_check.db ?

postfix/smtpd[1311]: fatal: open database /etc/postfix/client_checks.db: No such file or directory
postfix/smtpd[1352]: fatal: open database /etc/postfix/sender_checks.db: No such file or directory

You'll get this error if you specify check_client_access hash:/etc/postfix/client_checks in the smtpd_recipient_restrictions block and haven't ran the postmap /etc/postfix/client_checks command yet. You'll get a similar one for the sender_checks if you don't follow the full instructions in the whitelist blogpost.

smtpd check_relay_domains not set in smtpd_recipient restrictions

postfix/smtpd[1386]: fatal: parameter "smtpd_recipient_restrictions": specify at least one working instance of: check_relay_domains, reject_unauth_destination, reject, defer or defer_if_permit

If you get this error message, all you need to do is read it and follow what it tells you to do (add reject_unauth_destination to the smtpd_recipient_restrictions list) in /etc/postfix/main.cf. I'd recommend using "reject_unauth_destination" since you'll get the following warning if you use "check_relay_domains": 

postfix/smtpd[1505]: warning: support for restriction "check_relay_domains" will be removed from Postfix; use "reject_unauth_destination" instead

Credit where credit is due!

This blogpost drew heavily from the documentation as well as the new tutorial on creating a mailing list here which provides a quick reference point for the gist of setting up aliases within your system.