Stop the Spam: The Bulletproof Postfix Configuration Guide
Let's be honest: nobody wakes up in the morning excited to configure an email server. It is the trench warfare of systems administration. You are fighting a constant battle against RBLs (Real-time Blackhole Lists), script kiddies trying to turn your box into an open relay, and the unforgiving spam filters of major providers like Gmail and Hotmail.
I recently spent 48 hours migrating a client's legacy Sendmail setup to Postfix after their shared hosting IP got blacklisted. Their business literally stopped because their invoices were bouncing. The lesson? Your infrastructure is as vital as your configuration.
In this guide, we are going deep into configuring Postfix 2.7 on CentOS 5.5 to be secure, fast, and compliant with Norwegian standards.
Step 1: The Foundation (Infrastructure Matters)
Before touching a single config file, you need to verify your environment. The number one reason for poor deliverability isn't a typo in main.cf; it's a dirty IP address.
If you are hosting on cheap, oversold generic VPS providers, you are likely sharing a subnet with spammers. This ruins your "IP Reputation." At CoolVDS, we enforce strict abuse policies. This means when you grab a VPS in our Oslo datacenter, you get a clean IP that hasn't been burned by a neighbor sending pharma spam.
Pro Tip: Reverse DNS (PTR) is Non-Negotiable.
Most modern mail servers will reject your connection immediately if your IP address does not resolve back to your hostname. Ensure you set your PTR record in the CoolVDS control panel to match yourmyhostnamesetting.
Step 2: Installing Postfix on CentOS 5
First, purge the default Sendmail installation. It is 2010; we don't need m4 macros to configure a mailer anymore.
# yum remove sendmail
# yum install postfix
# alternatives --set mta /usr/sbin/sendmail.postfix
Step 3: The Critical Configuration
Open /etc/postfix/main.cf. This is where the magic happens. We are going to lock this down so tight that unauthorized relaying becomes impossible.
Basic Identity:
myhostname = mail.yourdomain.no
mydomain = yourdomain.no
myorigin = $mydomain
inet_interfaces = all
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
The Iron Gate (Relay Restrictions):
This is the most critical section. We want to accept mail for our users, and allow our trusted networks to send mail, but reject everything else.
smtpd_recipient_restrictions =
permit_mynetworks,
permit_sasl_authenticated,
reject_unauth_destination,
reject_rbl_client zen.spamhaus.org,
reject_rbl_client bl.spamcop.net
Notice the RBL lookups? By querying Spamhaus directly at the SMTP level, we drop connection attempts from known spammers before they waste our CPU cycles or disk I/O. On a high-traffic server, this efficiency is key.
Step 4: Handling Data and Latency
Email is I/O intensive. When you have a queue of 50,000 messages, disk latency becomes your bottleneck. While traditional SATA drives struggle here, high-performance RAID storage is essential.
For our Norwegian clients, latency is also physical. If your users are in Oslo or Bergen, hosting your mail server in Germany or the US adds unnecessary milliseconds to every SMTP handshake. CoolVDS offers local peering in Oslo, ensuring that connections from Telenor or NextGenTel are practically instant.
Step 5: Authentication and SPF
To prevent spoofing, you must implement SPF (Sender Policy Framework). While not a silver bullet, it validates that your server is authorized to send email for your domain.
Create a TXT record in your DNS zone:
yourdomain.no. IN TXT "v=spf1 mx a ip4:YOUR_IP_ADDRESS -all"
This tells the world: "Only the server at this IP is allowed to send mail for yourdomain.no. Drop everything else."
Compliance: The Norwegian Context
Operating in Norway brings specific legal obligations under the Personopplysningsloven (Personal Data Act). You are responsible for the security of the personal data (emails) flowing through your server. Using a provider like CoolVDS, which operates under Norwegian jurisdiction with strict physical security access to the hardware, simplifies your compliance posture significantly compared to US-based safe harbor hosts.
Conclusion
A mail server is a living entity. You must monitor /var/log/maillog like a hawk. But with a clean config, a valid SPF record, and the low-latency stability of a robust VPS, you stand a fighting chance.
Don't let sluggish disk I/O or bad IP reputation kill your delivery rates. Deploy a pristine CentOS 5 instance on CoolVDS today and get full control over your mail headers.