What steps should I take when setting up a new email server for outbound emails, and what are the best free MTA alternatives to Exim4?
Matthew Whittaker
Co-founder & CTO, Suped
Published 7 Jun 2025
Updated 19 Aug 2025
10 min read
Setting up a new email server for outbound emails is a significant undertaking that requires careful planning and execution. It is much more complex than simply installing a Mail Transfer Agent (MTA) and pressing send. Your success hinges on a robust infrastructure, proper configuration, and adherence to email best practices to ensure your messages reach their intended recipients without being flagged as spam.
The goal is to establish a credible sending reputation from day one. This involves more than just the server software, it encompasses your domain's DNS records, your IP address reputation, and how you manage your email lists. Missing crucial steps can lead to significant deliverability challenges, including emails landing in spam folders or being outright rejected by mailbox providers.
Many people opt for Exim4 due to its free nature, but it's important to understand its capabilities and limitations, especially for commercial sending. There are other excellent free MTA alternatives that might be better suited for modern email infrastructure and deliverability needs.
Initial network and MTA setup
Before you even install an MTA, foundational network and DNS configurations must be in place. These elements are critical for establishing trust with recipient mail servers and ensuring proper email routing. Without them, your emails are unlikely to reach the inbox, regardless of your content or sending volume.
Dedicated IP address: Obtain a clean, dedicated IP address from your hosting provider. Shared IPs can inherit a poor reputation from other senders, immediately impacting your deliverability.
Reverse DNS (PTR record): Configure a PTR record that matches your sending domain's forward DNS (A record). This record allows recipient servers to verify that the IP address sending the email is authorized for your domain. Ensure it's correctly set up with your hosting provider.
Firewall configuration: Open the necessary ports for email sending, typically SMTP (port 25, 465 for SMTPS, or 587 for Submission) and DNS (port 53). Restrict other ports to minimize security vulnerabilities.
Once your basic network configuration is ready, you can proceed with selecting and installing your MTA. This is the software that will handle the actual sending of your emails. After installation, careful configuration is required to ensure it adheres to modern email standards and best practices.
Email authentication: SPF, DKIM, and DMARC
Email authentication protocols are non-negotiable for modern email deliverability. They prove that your emails genuinely originate from your domain and haven't been tampered with. Ignoring these can lead to your emails being marked as spam or rejected by major mailbox providers, including Gmail and Yahoo Mail. Setting them up correctly is a foundational step for any new email server.
SPF record: Create an SPF record that lists all authorized IP addresses and domains that send email on your behalf. Publish this as a TXT record in your DNS.
DKIM signing: Implement DKIM signing to digitally sign your outgoing emails. This verifies that the email content hasn't been altered in transit and that it originates from your domain. Your MTA should be configured to do this automatically.
DMARC policy: Set up a DMARC policy to instruct recipient servers on how to handle emails that fail SPF or DKIM. Start with a p=none policy to gather reports, then gradually move to quarantine or reject as your confidence grows.
BIMI (optional): Consider implementing BIMI (Brand Indicators for Message Identification) to display your brand logo next to your emails in supporting inboxes, further building trust and brand recognition.
Best practices for email authentication DNS records
Consolidate SPF: Avoid exceeding the 10 DNS lookup limit for SPF. Combine multiple SPF records into one if necessary.
Ensure DKIM key length: Use a DKIM key length of at least 1024 bits, with 2048 bits preferred for stronger security.
Monitor DMARC reports: Regularly analyze DMARC reports to identify authentication failures and unauthorized sending.
Configuring these records correctly is vital. Misconfigurations can lead to emails being sent to spam or rejected. Make sure to double-check your DNS entries and use tools to validate them after publishing.
Reputation management and monitoring
Once your server is configured and authenticated, the focus shifts to maintaining a positive sender reputation. This is an ongoing process that involves monitoring your sending performance, managing your recipient lists, and responding to feedback.
IP warming: If using a new dedicated IP, start with low sending volumes and gradually increase them. This IP warming process helps mailbox providers build a positive reputation for your IP.
Bounce management: Implement a system to process bounce responses (hard and soft) and remove invalid email addresses from your mailing lists immediately. High bounce rates negatively impact your sender reputation.
Feedback loops (FBLs): Sign up for FBLs offered by major mailbox providers. These services notify you when recipients mark your emails as spam, allowing you to remove those users from your list and prevent further complaints. This proactive approach is crucial for maintaining a good sender reputation.
Maintaining a healthy sender reputation also means actively monitoring your standing with various email services. This includes keeping an eye on your Google Postmaster Tools data and checking if your IPs or domain appear on any email blocklists (or blacklists). Early detection of issues can prevent widespread deliverability problems.
Free MTA alternatives to Exim4
While Exim4 is a popular choice due to its open-source nature, it's often considered a legacy MTA, particularly for those looking to build a robust, modern sending infrastructure. It can lack built-in features that are standard in more contemporary MTAs, such as integrated bounce handling or streamlined DKIM signing. Fortunately, several free alternatives offer better features and a more modern architecture for outbound email.
When choosing an MTA, consider not just its initial setup but also its ongoing maintenance, performance for outbound email, and ease of integration with other systems, like bounce processing scripts. Here are some of the best free alternatives to Exim4 that are well-suited for modern outbound email servers:
Postfix: Postfix is a widely used, powerful, and secure MTA. It's known for its ease of configuration compared to Sendmail, and it offers excellent performance and flexibility. Many consider it a standard choice for Linux email servers due to its robust features and active community support. You can configure Postfix as a lightweight outgoing relay.
Sendmail: Sendmail is one of the oldest and most established MTAs. While incredibly powerful and configurable, it has a reputation for being complex to set up and manage, especially for newcomers. Its configuration file can be challenging to navigate, making it less beginner-friendly than Postfix. A comparison of Postfix vs Exim vs Sendmail is available for further research.
Haraka: Haraka is a modern, Node.js-based MTA designed for performance and extensibility. It's well-suited for high-volume sending and offers a more contemporary architecture compared to older MTAs. Its plugin-based system allows for significant customization, including integrated DKIM signing and bounce handling.
ZoneMTA: Developed with a focus on outbound mail, ZoneMTA is another modern, Node.js-based MTA that provides built-in bounce handling and DKIM signing capabilities. It's designed to be efficient for sending large volumes of email, making it a strong contender for those needing a dedicated outbound server.
OpenSMTPD: OpenSMTPD is part of the OpenBSD project, emphasizing security and simplicity. While it might have fewer features out-of-the-box compared to Postfix or Exim, its clean design and focus on correctness make it a solid choice for those prioritizing stability and a minimal footprint.
Each of these MTAs offers a unique balance of features, performance, and complexity. The best choice depends on your specific needs, technical expertise, and the volume of email you plan to send. For most modern outbound email operations, Postfix, Haraka, or ZoneMTA will provide more integrated features and easier management than Exim4.
Ongoing maintenance and list management
Beyond the technical setup, ongoing maintenance and careful list management are paramount. Mailbox providers are increasingly strict about sender behavior, and even minor missteps can lead to deliverability issues.
Regularly clean your email lists to remove inactive or invalid addresses. High bounce rates and spam complaints are major red flags. By maintaining a clean list and ensuring you only send to engaged recipients, you reinforce your positive sender reputation.
Additionally, staying informed about changes in email deliverability best practices and mailbox provider requirements is crucial. The email landscape is constantly evolving, with new rules and filtering algorithms being introduced regularly. Subscribing to industry newsletters and participating in forums can help you stay ahead of potential issues.
Views from the trenches
Best practices
Always set up a reverse DNS (PTR) record for your sending IP address, ensuring it matches your forward DNS record.
Implement SPF, DKIM, and DMARC authentication from day one. These are non-negotiable for deliverability.
Start with IP warming for any new dedicated IP, gradually increasing your sending volume over time.
Automate bounce processing to immediately remove invalid or hard-bouncing addresses from your mailing lists.
Common pitfalls
Neglecting PTR records, which often leads to immediate rejection by many mail servers due to lack of trust.
Failing to implement DMARC, SPF, and DKIM, or misconfiguring them, resulting in emails going to spam or being blocked.
Sending high volumes immediately from a new IP, triggering spam filters due to suspicious activity.
Not processing bounces, leading to high bounce rates and negatively impacting sender reputation over time.
Expert tips
For large scale outbound sending, consider MTAs like Haraka or ZoneMTA which offer modern architecture and built-in features for commercial senders.
Actively monitor your IP and domain on various blacklists (or blocklists) using automated tools.
Join industry groups or forums to stay updated on deliverability trends and share experiences with other email professionals.
Regularly audit your DNS records to ensure they are correct and optimized for email deliverability.
Marketer view
Marketer from Email Geeks says to ensure hard bounces and invalid recipients are removed immediately from the mailing list.
2023-02-21 - Email Geeks
Expert view
Expert from Email Geeks says Exim is more suited for organizational senders than commercial ones, and often lacks capabilities needed for high-volume email.
2023-02-21 - Email Geeks
Final thoughts on server setup
Setting up a new email server for outbound emails is a multifaceted process that extends far beyond simply choosing and configuring an MTA. It requires a deep understanding of DNS, email authentication protocols, and ongoing reputation management.
By prioritizing foundational steps like PTR records and firewall rules, meticulously implementing SPF, DKIM, and DMARC, and committing to continuous monitoring and list hygiene, you can establish a reliable outbound email system. While Exim4 serves its purpose, modern alternatives like Postfix, Haraka, or ZoneMTA offer more advanced features suitable for commercial and high-volume sending environments, often with better integrated deliverability functionalities.
Gmail and 
Yahoo Mail. Setting them up correctly is a foundational step for any new email server.
Postfix is a widely used, powerful, and secure MTA. It's known for its ease of configuration compared to Sendmail, and it offers excellent performance and flexibility. Many consider it a standard choice for Linux email servers due to its robust features and active community support. You can configure Postfix as a lightweight outgoing relay.
Sendmail is one of the oldest and most established MTAs. While incredibly powerful and configurable, it has a reputation for being complex to set up and manage, especially for newcomers. Its configuration file can be challenging to navigate, making it less beginner-friendly than Postfix. A comparison of Postfix vs Exim vs Sendmail is available for further research.
Haraka is a modern, Node.js-based MTA designed for performance and extensibility. It's well-suited for high-volume sending and offers a more contemporary architecture compared to older MTAs. Its plugin-based system allows for significant customization, including integrated DKIM signing and bounce handling.
OpenSMTPD is part of the OpenBSD project, emphasizing security and simplicity. While it might have fewer features out-of-the-box compared to Postfix or Exim, its clean design and focus on correctness make it a solid choice for those prioritizing stability and a minimal footprint.
