Sendmail More Domain Blacklisting to Prevent Spam

Combing through many free domain blackhole lists the following are relatively extensive, and are readily maintained.

combined.njabl.org

list.dsbl.org

dnsbl.sorbs.net

spam.dnsbl.sorbs.net

Using these blacklists in your sendmail configuration can reduce the spam received from the most common and prevailing sources. Combining these active spam prevention measures, with passive techniques spam can be greatly reduced. Passive spam prevention includes blackhole lists that are not controlled by you. You can also implement graphical active spam filtering using Mozilla Thunderbird via filters.

Sendmail Blackhole List - Eliminate Most Spam

To configure sendmail to automatically bounce most spam use one of the countless blackhole lists that are readily available, and consistently maintained:

http://www.declude.com/Articles.asp?ID=97

An excellent blackhole list is maintained by njabl.org. Use is relatively straight forward. Add the following line to the end of your sendmail.mc file, then recompile the sendmail configuration file.

FEATURE(dnsbl,`combined.njabl.org',`Message from $&{client_addr} rejected - see http://njabl.org/lookup?$&{client_addr}')

For more detailed information on how to use this blackhole list you can visit their website directly:

http://njabl.org/use.html

I used to get well over 150 spam messages per day. Now I maybe get 5 total

Thunderbird - Built in Spamassasin

Using Thunderbird, in conjunction with your IMAP configured dovecot is by far the best method of synchronizing you mail folder with multiple devices. In Thunderbird you should instantly turn on your junk mail “adaptive filters”. You can also set custom filter rules to send messages with particular words in the header to the junk folder. Frankly I prefer using the graphical configuration of Thunderbird to the direct command line configuration of spamassasin. Thunderbird is powerful, and successfully filters out well over 95% of the spam I receive. I get closer and closer every day to completely avoiding all spam. Every day I set a new filter rule, and mark new messages as spam.

Ubuntu Sendmail Boot Bug

There are two bugs that I currently aware of regarding the sendmail boot process. The first and simplest deals with your hostname. In Ubuntu, the default configuration of sendmail and apache required a fully qualified domain name. You can adjust your FQDN manually in the /etc/hostname file. The proper format is:

name.domain.com

Save the file, and you will not get any errors on an apache or sendmail reboot. Also there is sometimes an issue when sendmail tries to reconfigure its cf file during boot. I don’t experience this issues, but its worth mentioning due to its simple workaround. Just delete the two following files, and sendmail will not re-configure on boot (you will have to do it manually if you change its settings):

/etc/network/if-down.d/sendmail

/etc/network/if-up.d/sendmail

Debian Sendmail Virtusertable

On Fedora the virtusertable and virtual-domains files are pre-configured. On Debian you must add the following lines to your sendmail.mc file:

FEATURE(`virtusertable’, `hash /etc/mail/virtusertable’)dnl

VIRTUSER_DOMAIN_FILE(`/etc/mail/virtual-domains’)dnl

After adding these two lines create the virtusertable and virtual-domains files using nano:

sudo nano /etc/mail/virtusertable

Save the file and exit by pressing control “o” and then control “x”.

Do the same for the virtual-domains file, and them you can populate both accordingly.

The virtusertable is highly useful if you are hosting multiple domains (virtualhosting). You will be able to configure multiple email addresses, at multiple domains, to be forwarded to a particular local user.

Dovecot User Configuration

There is really nothing to configure with Dovecot. Once its installed, configured, and running it will automatically accecpt logins from any user on the local machine. I highly recommend the following simple configuration:

mail_location = mbox:~/mail:INBOX=/var/mail/%u

By setting up Dovecot like this, users on the local machine can login to access their mailbox. Simple and straight forward. No you have to configure Sendmail to deliver and send mail from this configured location. Some more information, about Dovecot and Sendmail configuration, can be found in my previous posts:

http://www.bgevolution.com/blog/index.php/dovecot-inter-config-with-sendmail/

Sendmail - Consolidate Multiple Domains

Sendmail has the virtusertable configuration file, that is built into the virtusertable.db file. The purpose of this file is to direct incoming email, for a particular domain, to a particular user. If you have multiple domains, you can separate the email login proceedures by specifying a different user name for each respective domain. Such a configuration would look like this:

@bgevolution.com bgevolution

@nodomain.com nodomain

In this type of configuration you would have a user “bgevolution” and a user “nodomain”, and you will be able to login to Dovecot separately for each one. Another configuration consolidates things a bit:

@bgevolution.com primaryuser

@nodomain.com primaryuser

In this configuration you will be able to login to Dovecot, as primaryuser, which will contain all mail sent to both bgevolution.com and nodomain.com.

Also note that in these examples I have used no text prior to the “@” symbol. In this way your Sendmail will catch all incoming mail to either domain. If you want to restrict things a bit you can add your username; in this way only email, coming specifically to that user name, will be accepted.