How can I hide my mail server IP address or mitigate attacks against it?
Michael Ko
Co-founder & CEO, Suped
Published 27 Apr 2025
Updated 16 Aug 2025
7 min read
For many, the idea of hiding a mail server's IP address stems from a desire for enhanced security and protection against relentless cyber attacks. Whether it's to avoid Distributed Denial of Service (DDoS) attacks or shield against sophisticated phishing attempts and email listbombing, the motivation is understandable. However, achieving complete anonymity for a mail server's IP is generally not feasible, nor is it advisable for legitimate email operations.
Email protocols, by their very nature, require sender IP addresses to be transparent in email headers, particularly in the Received headers. This transparency is crucial for email deliverability and combating spam, allowing receiving mail servers to trace the message's path and verify its authenticity. Attempting to obscure this information can, in fact, raise a red flag with Internet Service Providers (ISPs) and Mailbox Providers (MBPs), potentially leading to deliverability issues, including your emails landing in spam folders or your IP being placed on a blocklist (or blacklist). The focus, therefore, shifts from hiding to robust mitigation and protection strategies.
Why mail server IPs are exposed
Mail server IP addresses are inherently public due to how email delivery works. When you send an email, your Mail Exchange (MX) record points to your mail server's hostname, which then resolves to its public IP address. This IP is recorded in the email's headers as it travels from server to server. This is a fundamental aspect of the Simple Mail Transfer Protocol (SMTP) and ensures accountability across the email ecosystem.
You might consider using services like Cloudflare to hide your web server's IP, but this functionality does not extend to MX records. Cloudflare primarily acts as an HTTP proxy, not an SMTP proxy. While your MX record might point to a hostname whose A record is proxied by Cloudflare, this proxying mechanism doesn't work for email traffic itself. The mail server's true IP will still be revealed in the Received headers of the emails sent through it.
Example of an email header showing the mail server's IP addressplaintext
Received: from mail.example.com ([192.0.2.1]) by recipient.com with ESMTPSA id ABC123DEF456;
Tue, 28 Nov 2222 10:00:00 -0500 (EST)
Any attempt to fully hide your mail server's IP address from the email headers would likely break email functionality or severely impact deliverability. Mailbox providers rely on these IP addresses for reputation scoring, spam filtering, and enforcing email authentication protocols like SPF, DKIM, and DMARC. Hiding it could trigger automated spam filters, as it resembles tactics used by spammers and malicious actors.
Mitigating attacks on your mail server
Instead of trying to hide your IP, the optimal approach is to focus on strengthening your mail server's defenses and maintaining a robust security posture. Many attacks target email servers, ranging from email listbombing and bot sign-up attacks to brute-force login attempts and DDoS attacks. These can overwhelm your server, making it unable to receive legitimate emails or even bringing it offline. Implementing comprehensive security measures is key to mitigating these threats.
One crucial step is to ensure your mail server is not configured as an open relay. An open relay allows any external source to send emails through your server, making it a prime target for spammers and phishing campaigns. Closing open relays prevents your server from being exploited for malicious purposes, which can lead to your IP address being blacklisted and severe deliverability issues. Configuring strict mail relay options to only allow authorized IP addresses to send mail is a foundational security practice. You can learn more about securing your email server against attacks from resources like Ctemplar's guide on email server security.
To combat DDoS and similar IP-level attacks, consider placing your mail server behind an Intrusion Detection System (IDS) or Intrusion Prevention System (IPS) device. These systems monitor network traffic for suspicious activity and can block malicious connections, protecting your server from being overwhelmed. While this doesn't hide your IP, it acts as a robust shield, filtering unwanted traffic before it reaches your mail server. You can also implement local IP blocklists to deny access from known problematic IP addresses.
Leveraging email authentication and external services
Implementing strong email authentication standards is paramount for both security and deliverability. SPF, DKIM, and DMARC records verify that emails originating from your domain are legitimate and have not been tampered with. This helps prevent email spoofing and phishing attacks, where attackers try to impersonate your domain.
For organizations facing frequent attacks or those without the resources to manage a self-hosted mail server securely, outsourcing email to a large-scale third-party provider is an excellent strategy. Companies like Google Workspace or Microsoft 365 have robust infrastructure and dedicated security teams designed to handle large volumes of traffic and mitigate various types of attacks, including DDoS and email bombing. This shifts the burden of server maintenance and security to experts.
Self-hosting email server
Control: Complete control over server configuration and data.
Complexity: Requires significant technical expertise for setup, maintenance, and security.
Security responsibility: You are entirely responsible for implementing all security measures.
Attack mitigation: Requires dedicated hardware/software like firewalls, IDS/IPS, and constant monitoring.
Utilizing a smart host or an email gateway service can also help. These services act as intermediaries, routing your outgoing mail through their infrastructure. While your original server's IP might still be visible in some internal headers, the external-facing IP for reputation purposes would be that of the smart host, which typically has advanced spam and attack filtering capabilities. This can provide a layer of abstraction and protection.
Proactive measures for reputation and security
Beyond technical configurations, proactive measures are vital for safeguarding your mail server. Regularly updating your mail server software and operating system patches vulnerabilities that attackers could exploit. Strong password policies and multi-factor authentication for all email accounts and server access are non-negotiable.
Monitoring your mail server's reputation and checking for blocklist (blacklist) listings is also critical. If your IP address or domain gets listed on a DNSBL (DNS-based blocklist), your emails will likely be rejected by many receiving mail servers. Use a blocklist checker regularly and address any listings promptly. Understanding how email blacklists work can help you prevent getting listed and recover quickly if you are.
Common attack types
DDoS attacks: Overwhelming server with traffic, causing downtime.
Email bombing: Flooding inboxes or servers with massive volumes of emails.
Open relay abuse: Using unsecure servers to send spam.
Brute-force attacks: Guessing login credentials to gain unauthorized access.
Mitigation strategies
Implement firewalls/IDS/IPS: Block malicious traffic at the network edge.
Configure anti-spam filters: Filter out unwanted bulk emails at the server level.
Close open relays: Prevent unauthorized third-party email sending.
Use strong authentication: Implement robust passwords and multi-factor authentication.
Educating your users about phishing, malware, and other social engineering tactics is also an underrated but essential layer of defense. A vigilant user base can be your first line of defense against attacks that bypass technical security measures. Regularly reviewing and updating your email security policies is also crucial to adapt to evolving threats. For more security tips, you can check out Vircom's top 11 tips for securing your email server.
Views from the trenches
Best practices
Maintain strong email authentication records, including SPF, DKIM, and DMARC, to prevent spoofing.
Regularly monitor your server logs for unusual activity and implement automated alerts for suspicious patterns.
Use a robust email security gateway or service to filter incoming and outgoing mail for threats.
Ensure your mail server software and operating system are always up to date with the latest security patches.
Educate your users on phishing awareness and secure email practices to reduce human error vulnerabilities.
Common pitfalls
Attempting to completely hide your mail server's IP address, which can negatively impact deliverability.
Neglecting to close open mail relays, making your server a target for spammers and blocklisting.
Not monitoring for IP blocklist (blacklist) listings, leading to emails being rejected by recipients.
Relying solely on network firewalls without implementing application-level email security.
Failing to implement multi-factor authentication for server access and privileged accounts.
Expert tips
Consider using a dedicated mail relay service for outbound email if you experience frequent outbound issues.
Implement rate limiting on SMTP connections to prevent email bombing and brute-force attacks.
Utilize a robust IDS/IPS system to protect your server from IP-level DDoS attacks.
If self-hosting, segment your network and isolate your mail server for enhanced security.
Regularly audit your email server's security configuration against best practices and compliance standards.
Expert view
Expert from Email Geeks says that Cloudflare primarily functions as an HTTP proxy, and its proxying capabilities do not extend to SMTP traffic, meaning it cannot hide the mail server's IP address.
2023-03-15 - Email Geeks
Marketer view
Marketer from Email Geeks says that for organizations experiencing frequent email server attacks, investing in a more capable Mail Transfer Agent (MTA) platform can significantly help mitigate these threats.
2023-07-22 - Email Geeks
Prioritizing security over concealment
While the desire to hide a mail server IP address is understandable for security reasons, it's largely impractical and counterproductive for legitimate email operations. The underlying architecture of email requires IP transparency for proper routing, authentication, and spam prevention.
Instead, the focus should be on robust security and mitigation strategies. By implementing strong network defenses, configuring your mail server securely, maintaining proper email authentication, and potentially leveraging third-party email services, you can effectively protect your mail server from attacks and ensure your emails reach their intended recipients without being blocked or blacklisted.
Google Workspace or 
Microsoft 365 have robust infrastructure and dedicated security teams designed to handle large volumes of traffic and mitigate various types of attacks, including DDoS and email bombing. This shifts the burden of server maintenance and security to experts.
