Monitoring SMTP server (using mailgraph, qshape and postqueue

Monitoring SMTP mails never been easier! You can check the number of sent emails, bounced emails, rejected emails and etc (you can see demo at http://www.stat.ee.ethz.ch/mailgraph.cgi).

Let’s get the source:

wget http://mailgraph.schweikert.ch/pub/mailgraph-1.14.tar.gz
tar xf mailgraph-1.14.tar.gz
mv mailgraph-1.14 /var/mailgraph

and install dependencies:

yum install perl-rrdtool
yum install perl-File-Tail

and run the mailgraph once to fetch the previous logs:

./mailgraph.pl -l /var/log/maillog -c -v

then run it as service:

cp mailgraph.pl /usr/local/bin/
./mailgraph-init start

Now the cgi file is needed to be executed by web server so once we installed the web server we will configure CGI configs. The main changes are AddHandler, Add ExecCGI to “/var/mailgraph” directory and add mailgraph.cgi as an index file like index.php.

yum install httpd
cp /etc/httpd/conf/httpd.conf /etc/httpd/conf/httpd.conf.original
vi /etc/httpd/conf/httpd.conf (appendix 01)
service http start
chkconfig httpd on

Now you should be able to browse the web server and see the stats. I have to note that the stats are not getting updated frequently. I coolant figure out how frequent this is getting updated but sometimes I had to run the mailgraph script manually to get latest stats. At this moment we are done with mailgraph.

Now we just take a look at shape and other CLI tools for monitoring SMTP. qshape and post queue are two useful scripts found in postfix additional scripts. We need to install it first:

yum install postfix-perl-scripts

And here are some example of the tool to get the stat of different queues:

qshape hold
qshape deferred
qshape active

postqueue is another tool:

postqueue -p
postqueue -p | egrep -c "^[0-9A-F]{10}[*]"
postqueue -p | egrep -c "^[0-9A-F]{10}[^*]"

we also can use the maillot directly with assistance of grep:

grep -c "postfix/smtp.*status=sent" /var/log/maillog 
grep -c "postfix/smtp.*status=bounced" /var/log/maillog

Continue reading

Deploying SMTP server using Postfix and OpenDKIM

Days ago we got some issue with Amazon SES and decide to make our own SMTP relay service. I tried the combinations of sendmail with dim-milter but for some reason I could not make it work so I start another server from scratch which did work this time. This post mainly focus on configuring OpenDKIM as Postfix is fairly straightforward.

The first thing to do is disabling sendmail which is the default SMTP client on Amazon Linux:

service sendmail stop
chkconfig sendmail off

And then installing Postfix and configuring it:

yum install postfix
cp /etc/postfix/main.cf /etc/postfix/main.cf.original 
vi /etc/postfix/main.cf (appendix 01)

Configuration mainly involves adding DKIM settings (such as milter socket info) and modifying receptions restrictions. In the new setting we define sender_access file to contain the list of senders who can relay through our SMTP service.

cat "DOMAIN.COM OK" >> /etc/postfix/sender_access
postmap /etc/postfix/sender_access

Now we are done with Postfix so it is better to check by sending a test mail.

service postfix start
chkconfig postfix on

The main concern of this post, DKIM, is to cryptographically validate the sender is really from that domain (i.e. domain.com). The validation process starts with the SMTP server signing the email using its private key and then the destination mail server tries to match the private key with the public key obtained from senders’ claimed domain DNS. Once the private and public key matched then it means the SMTP server is from the domain it claims to be.

To install the DKIM we need some API from sendmail and openssl:

yum install sendmail-devel openssl-devel

openDKIM is not available in default repository so we will add it and then install it:

rpm -Uvh http://mirror.pnl.gov/epel/6/i386/epel-release-6-8.noarch.rpm
yum --disablerepo=* --enablerepo=epel install opendkim

Once installation finished we proceed to configurations. There are 3 main files to configure: opendkim.conf contains the main configs such as address of signing table file, key table file and the socket address to listen. The key table file contains the list of keys. The signing table defines which domains should be signed by which key. You will also need to add trusted IP addresses of senders in /etc/opendkim/TrustedHosts to grant them access to SMTP.

cp /etc/opendkim.conf /etc/opendkim.conf.original
vi /etc/opendkim.conf (appendix 02)
vi /etc/opendkim/KeyTable  (appendix 03)
vi /etc/opendkim/SigningTable (appendix 04)

Now we need to generate a pair of keys (private and public) which the public key will be added into DNS records of send domain:

mkdir /etc/opendkim/keys/DOMAIN.COM
opendkim-genkey -D /etc/opendkim/keys/DOMAIN.COM/ -d DOMAIN.COM -s default
mv /etc/opendkim/keys/DOMAIN.COM/default.private /etc/opendkim/keys/DOMAIN.COM/default
chown -R opendkim:opendkim /etc/opendkim/keys/DOMAIN.COM
cat /etc/opendkim/keys/DOMAIN.COM/default.txt

Then start the service:

service opendkim start
chkconfig opendkim on

Finally, you have to add a TXT record in your DNS dashboard. The record name should be default._domainkey.DOMAIN.COM and it should contains something like the following (based on the /etc/opendkim/keys/DOMAIN.COM/default.txt):
“v=DKIM1; g=*; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDHY7Zl+n3SUldTYRUEU1BErHkKN0Ya52gazp1R7FA7vN5RddPxW/sO9JVRLiWg6iAE4hxBp42YKfxOwEnxPADbBuiELKZ2ddxo2aDFAb9U/lp47k45u5i2T1AlEBeurUbdKh7Nypq4lLMXC2FHhezK33BuYR+3L7jxVj7FATylhwIDAQAB”

/etc/postfix/main.cf (appendix 01)

smtpd_milters           = inet:127.0.0.1:2525
non_smtpd_milters       = $smtpd_milters
milter_default_action   = accept

smtpd_error_sleep_time = 1s
smtpd_soft_error_limit = 10
smtpd_hard_error_limit = 20

smtpd_recipient_restrictions = 
	 permit_mynetworks
	 check_sender_access hash:/etc/postfix/sender_access
	 reject_unauth_destination

queue_directory = /var/spool/postfix
command_directory = /usr/sbin
daemon_directory = /usr/libexec/postfix
data_directory = /var/lib/postfix
mail_owner = postfix

inet_interfaces = all
inet_protocols = all

mydestination = $myhostname, localhost.$mydomain, localhost
unknown_local_recipient_reject_code = 550

alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases

debug_peer_level = 2
debugger_command =
	 PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin
	 ddd $daemon_directory/$process_name $process_id & sleep 5

sendmail_path = /usr/sbin/sendmail.postfix
newaliases_path = /usr/bin/newaliases.postfix
mailq_path = /usr/bin/mailq.postfix
setgid_group = postdrop
html_directory = no

manpage_directory = /usr/share/man
sample_directory = /usr/share/doc/postfix-2.6.6/samples
readme_directory = /usr/share/doc/postfix-2.6.6/README_FILES

/etc/opendkim.conf (appendix 02)

Canonicalization        relaxed/relaxed
ExternalIgnoreList      refile:/etc/opendkim/TrustedHosts
InternalHosts           refile:/etc/opendkim/TrustedHosts
KeyTable                refile:/etc/opendkim/KeyTable
LogWhy                  Yes
MinimumKeyBits          1024
Mode                    sv
PidFile                 /var/run/opendkim/opendkim.pid
SigningTable            refile:/etc/opendkim/SigningTable
Socket                  inet:2525@127.0.0.1
Syslog                  Yes
SyslogSuccess           Yes
TemporaryDirectory      /var/tmp
UMask                   022
UserID                  opendkim:opendkim

/etc/opendkim/KeyTable (appendix 03)

default._domainkey.DOMAIN.COM:default:/etc/opendkim/keys/DOMAIN.COM/default

/etc/opendkim/SigningTable (appendix 04)

*@DOMAIN.COM default._domainkey.DOMAIN.COM