How to resolve a 'connection refused' network error when sending emails?

Key findings

• Network issue: The 'connection refused' error is fundamentally a network communication problem, not a typical SMTP bounce or email block.
• No connection established: It means the sending server was unable to initiate a TCP connection with the receiving server on the designated port (usually 25, 465, or 587).
• Distinction from blocks: This error is different from being on an email blacklist or blocklist, which typically results in a bounce message with a specific rejection code, as explained in our guide what does it mean when your email is blacklisted?.
• Server-side rejection: It implies that the target server (or a firewall in front of it) actively refused the connection attempt.

Key considerations

• Initial diagnosis: Begin by checking basic network connectivity. Can your server ping or traceroute to the recipient's mail server IP address?
• Port availability: Verify that the necessary SMTP port (e.g., 25, 465, 587) on the recipient's server is open and listening. You can try to connect manually using tools like Telnet or Netcat.
• Firewall interference: Ensure that your own server's firewall or network security groups are not blocking outbound connections on standard SMTP ports. Similarly, the recipient's firewall could be blocking your IP, as Kinsta explains in their guide on how to fix the ERR_CONNECTION_REFUSED error.
• DNS issues: Incorrect or outdated MX records can lead to attempts to connect to the wrong server, causing connection refusals. Confirm the MX records are correctly configured for the recipient domain.
• Server status: The recipient's mail server might simply be offline, overloaded, or not running its mail service.
• Further troubleshooting: For more in-depth network diagnostics, consult our article on how to troubleshoot connection refused email delivery errors.

Key opinions

• Initial confusion: Marketers frequently interpret 'connection refused' as a form of blacklisting or a general bounce, seeking delisting instructions.
• Lack of bounce message: The absence of a specific bounce error message makes troubleshooting challenging for those less familiar with network diagnostics.
• Server-side focus: Many marketers correctly infer that the issue originates from their sending server's inability to reach the recipient, often asking how to proceed from that point.
• Seeking external help: There's a strong tendency to ask for help from community forums or support channels when faced with this type of technical error.

Key considerations

• Review error logs: Although not a bounce, your sending server's logs should contain details about the network refusal. This is the first place to check for specific error codes or IP addresses.
• Basic connectivity checks: Confirm that your internet connection is stable and that there are no typos in the SMTP server details or port numbers, as suggested by Mailgun's guide on understanding email failed to send messages.
• Sender environment: Check if any local firewalls, proxy settings, or VPN services on your sending system are interfering with outgoing connections, a common cause highlighted in DreamHost's article on fixing connection refused errors.
• Server resource limits: Sometimes, a high volume of connections from your server can lead to refusals, which might be related to issues like those seen with Postfix's too many connections errors.
• Seek technical assistance: If initial checks don't reveal the problem, contacting your email service provider or hosting support is advisable.

Key opinions

• Not an SMTP block: Experts clearly state that 'connection refused' is a network error, not an SMTP-level error or an indication of being on a blocklist.
• Inability to reach: The error signifies that the sending server simply cannot reach the receiving server at all, implying a route or availability problem.
• Diagnostic first: The immediate steps recommended involve network diagnostics such as manually attempting a connection on port 25, tracerouting, or pinging the IP address.
• MX gateway importance: Identifying and contacting the administrator of the recipient's MX gateway (like synaq.com in the provided scenario) is often necessary for resolution.

Key considerations

• Verify recipient's status: It is crucial to determine if the recipient's mail server is indeed online and configured to accept connections on the expected SMTP port.
• Routing issues: Problems with network routing tables on either end of the connection path can cause these errors, preventing packets from reaching their destination.
• Firewall configuration: Both sender and receiver firewalls must allow SMTP traffic on the correct ports. Misconfigurations are a frequent cause of connection refusals, which can lead to larger deliverability issues as highlighted in our expert guide to improve email deliverability.
• Temporary vs. deliberate: Experts stress the need to distinguish between a transient routing or TCP failure and a deliberate network block (which is different from a typical IP blacklist). This often requires more advanced network analysis.
• Contacting recipient's host: If initial diagnostics confirm reachability issues, direct communication with the recipient's mail hosting provider or network administrator is often the most effective way to resolve the issue, especially for problems like those seen with SMTP connection refused errors on AWS.

Key findings

• Active refusal: Documentation confirms that 'connection refused' implies the target system explicitly rejected the connection, unlike a timeout where no response is received.
• Common causes: Frequent culprits include the mail server process not running, an incorrect port number being used, or firewall rules blocking the connection.
• Security settings: Web hosting server security settings are often cited as a source of refusal, either blocking specific IPs or ports.
• SMTP plugin failure: For email applications or plugins, the error often means the software failed to connect to the mail server on the expected SMTP port.

Key considerations

• Server availability: Always ensure the mail server software (e.g., Postfix, Exim) is running and configured correctly on the intended ports.
• Port configuration: Confirm that the application is attempting to connect to the correct SMTP port (25 for standard, 465 for SMTPS, 587 for Submission) and that the server is listening on that port, as detailed by SendLayer's documentation on connection refused errors.
• Firewall rules: Review firewall rules on both the sending and receiving servers, including cloud security groups, to ensure SMTP traffic is permitted.
• DNS resolution: Proper DNS resolution, including correct MX records, is fundamental for directing email traffic. Errors here can lead to connection attempts to incorrect or non-existent hosts.
• Authentication checks: While 'connection refused' is not typically an authentication error, ensuring proper SPF, DKIM, and DMARC setup, as described in our simple guide to DMARC, SPF, and DKIM, is vital for overall deliverability.