Setting up an email server on Linux is relatively straightforward, but the process doesn't end there. We've seen instances where a misconfigured mail gateway led to an open relay, allowing a spammer attack. It's crucial to exercise extra caution when handling services like web and email.
1. MX Record
The Mail Exchanger (MX) record is essential for email-related information in your DNS. It directs email servers on how to route your emails. If you're hosting your own DNS server, don't forget to add an MX record. You can test your MX record by switching your internal DNS to an external one.
2. IP Address
Use the mail security tool below to check the status of your IP:
MXToolbox SuperTool
3. Secure Mail Test Tool
Use this tool to run a secure mail test:
CheckTLS
4. Reverse DNS
Anti-spam applications typically check for a valid reverse DNS IP. If you're sending emails from a mail server without a reverse DNS, your mail reputation will suffer compared to servers with a valid reverse DNS. The negative impact may not be immediate, but over time, it can result in bulk emails being blocked or your IP being blacklisted.
5. SPF DNS Record
Many anti-spam applications and gateways perform Sender Policy Framework (SPF) checks. SPF adds an extra layer of spam filtering, verifying whether the email genuinely originates from the claimed domain. It's highly recommended to include an SPF record in your DNS for enhanced protection.
