How to troubleshoot email bounce issues with Charter/Spectrum due to concurrent connections?
Summary
What email marketers say11Marketer opinions
Email marketer from Gmass shares that using multiple sending domains can help distribute the sending load and avoid hitting connection limits with a single domain. Rotate domains to prevent any one from being throttled.
Email marketer from Mailjet shares that segmenting email lists and sending targeted campaigns can improve engagement and reduce the likelihood of bounces. Sending relevant content helps maintain a good sender reputation.
Email marketer from StackOverflow suggests using tools like `telnet` or `netcat` to manually test connections to Spectrum's mail servers to diagnose connection issues. They recommend checking for error messages that indicate connection limits.
Email marketer from Litmus explains that monitoring bounce rates helps identify issues with deliverability, including connection-related bounces. High bounce rates can indicate problems with throttling or reputation.
Email marketer from SuperUser responds that you should check error logs to see what is causing the errors. The log should show you if the error is to do with too many connections, or something else.
Email marketer from MXToolbox advises to use their online tools to check the sender's email server configuration, including DNS records (SPF, DKIM, DMARC) and blacklist status, as these can impact deliverability and trigger connection limits.
Marketer from Email Geeks clarifies that the bounce issue is not a traditional throttle, but rather the MTA is opening too many connections at once.
Email marketer from EmailOnAcid shares that slowly warming up new IP addresses helps build a positive reputation and avoid being flagged for sending too many connections too quickly. Start with a small volume and gradually increase it.
Email marketer from Reddit advises users to check their sending infrastructure and ensure they are properly throttling connections. They suggest gradually increasing sending volume to avoid triggering connection limits.
Email marketer from Email Geeks confirms they are on a dedicated IP and their ESP is resistant to changing things, but they should lean on them due to the ongoing issue.
Marketer from Email Geeks expresses surprise that this isn't part of the ESP's default traffic shaping rules.
What the experts say4Expert opinions
Expert from Email Geeks suggests talking to the ESP and that it's a reasonably simple config change. They also ask if they're on a dedicated IP.
Expert from Email Geeks asks what the reason for the bounce is, as Charter/Spectrum usually provide a reason for non-delivery.
Expert from Spam Resource, Steve Jones, answers that senders should work with their ESPs to properly configure connection limits and ensure they are not exceeding the thresholds set by Charter/Spectrum. He also recommends monitoring error logs for specific messages related to connection limits.
Expert from Word to the Wise, Laura Atkins, explains that throttling is a common practice among ISPs like Charter/Spectrum to protect their users. Senders experiencing bounce issues due to concurrent connections should focus on building and maintaining a good sender reputation to avoid being throttled aggressively.
What the documentation says4Technical articles
Documentation from Postfix.org explains the `smtp_destination_concurrency_limit` parameter, which controls the maximum number of concurrent connections to a single destination. Adjusting this setting can help manage concurrent connections.
Documentation from Spectrum Support explains that Spectrum limits the number of concurrent connections to prevent spam. They recommend reducing the number of connections and trying again later.
Documentation from Sendmail explains that Sendmail supports connection rate limiting through the `ConnectionRateThrottle` option. This can be configured to limit the number of connections from a single IP address per unit time.
Documentation from RFC Editor explains that RFC 5321 provides guidelines for SMTP connection management, including recommendations for connection establishment, maintenance, and termination. It emphasizes the importance of graceful connection handling to avoid issues.