What exactly is email throttling by Charter.net?

Throttling means Charter.net is intentionally slowing down the delivery of your emails due to their assessment of your sending patterns or volume. It's distinct from a hard block or blacklist (or blocklist) because messages are still delivered, albeit with significant delays. This usually happens to manage server load or to flag potentially suspicious, albeit not outright spam, traffic.

What does the AUP#In-1310 error from Charter.net signify?

The AUP#In-1310 error indicates that your sending behavior (e.g., volume, connection rate) is violating Charter.net's Acceptable Use Policy for inbound email. It's their system's way of telling you that you're sending too much or too fast, even if your overall sender reputation is good with other ISPs. It generally results in a deferral, not a hard bounce.

My organization uses dedicated IPs with a solid reputation. Why am I still throttled?

While a dedicated IP shows a strong commitment to your sending reputation, Charter.net may have different thresholds. A dedicated IP means your sending reputation is isolated, but if the volume to Charter.net itself is too high or spikes suddenly, it can still trigger their specific throttling mechanisms, regardless of how other ISPs perceive your traffic.

Should I adjust my sending rate and connection limits specifically for Charter.net?

Yes, you should. The most effective way to resolve throttling is to gradually increase your sending volume to Charter.net over time. Start with a volume below their observed limit, and slowly increment it as their systems become accustomed to your traffic. Avoid large, sudden spikes in email volume to their domains, especially during peak sending periods.

How to resolve email throttling issues with Charter.net when sending high volumes of email? - Troubleshooting - Email deliverability - Knowledge base

Email throttling from internet service providers (ISPs) like Charter.net, now known as Spectrum, is a common challenge for senders, especially those dealing with high email volumes. It means that while your emails aren't outright rejected, their delivery is deliberately slowed down. This can be particularly frustrating for organizations, such as non-profits during critical campaigns like Giving Tuesday, where timely delivery is crucial.

Even if your overall sender reputation appears pristine on platforms like

Google Postmaster Tools or

SNDS, and your email authentication protocols like SPF, DKIM, and DMARC are correctly configured, you might still encounter specific issues with Charter.net. Their systems can have unique criteria for assessing incoming mail streams, leading to throttling responses even when broad reputation metrics are positive. This is a common hurdle for businesses and non-profits alike.

Understanding why this happens and what steps you can take is crucial. My goal is to shed light on Charter.net's specific throttling mechanisms and provide actionable strategies to help your high-volume email campaigns reach their intended recipients without significant delays or blockages.

Understanding Charter.net's throttling mechanisms

When Charter.net (Spectrum) throttles your emails, you often receive an SMTP response similar to the one below. The AUP#In-1310 error code indicates that the sender has violated Charter's Acceptable Use Policy related to inbound email, often due to perceived high volume or suspicious connection patterns. It is important to note that this is not always a direct blacklist or blocklist, but rather a rate or concurrency limit in response to perceived threats or policy breaches.

Charter.net SMTP rejection responsetext

"550 5.1.0 <foo@SMTP.MAILFROM DOMAIN> sender rejected. Please see https://www.spectrum.net/support/internet/understanding-email-error-codes for more information. AUP#In-1310" received from pkvw-mx.msg.pkvw.co.charter.net (47.43.26.7)

The key here is that different ISPs, including Charter.net, have varying reputation standards. What might be considered acceptable sending behavior for

Gmail or

Yahoo (formerly Charter.net's partner) might trigger a throttling response from Charter's mail servers. Their policies can be more stringent, especially when detecting sudden spikes in volume or consistent high connection rates from a specific IP address or domain.

This leads to a distinction between rate limits and concurrency limits. Rate limits restrict the number of emails sent per unit of time (e.g., messages per minute), while concurrency limits restrict the number of simultaneous connections. Charter.net often employs a combination, and hitting either limit can result in deferrals and the AUP#In-1310 error.

Diagnosing the root cause

Even with a seemingly perfect reputation across major mail providers, Charter.net might perceive your sending patterns differently. This isn't necessarily a false positive, but rather an indication that their filtering systems have a specific threshold or algorithm that your current volume or connection rate is exceeding. The critical factor is aligning your sending practices with Charter's expectations.

Sender's perspective

Overall reputation: IPs and domains show solid green on major reputation tools.
Compliance: All email authentication (SPF, DKIM, DMARC) is correctly configured.
Bounce rates: Very low, indicating a clean list and good engagement with other providers.

Charter.net's perspective

Volume spikes: Sudden or consistently high email flow to their network triggers automated defense.
Connection patterns: Too many concurrent connections or rapid sending attempts can be flagged.
Hidden reputation factors: Internal metrics, spam trap hits, or user complaints specific to Charter.net.

One area to investigate is the SMTP MAILFROM string. While your From header might be well-aligned, the underlying SMTP MAILFROM address could be a factor. Charter.net may be evaluating the reputation associated with this specific address, especially if it is tied to shared infrastructure or domains that have previously shown problematic sending behavior on their network. Their troubleshooting guides often point to general issues, but the specific `AUP#In-1310` error indicates a policy breach related to how you're sending.

Strategies for high-volume senders

When facing persistent throttling from Charter.net, even with optimal overall reputation, the primary strategy involves adapting your sending behavior specifically for their network. This often means adjusting your email sending rates. If Charter.net is only accepting 60-65 messages per hour before deferring connections for an hour, continuing to send at a higher rate will not improve the situation. Instead, it can entrench the negative perception of your sending IP.

A crucial aspect of high-volume sending is gradually increasing your volume, known as IP warming. While your IPs might be sufficiently warmed for other providers, Charter.net's specific filters might require a more conservative approach or a separate warming process focused solely on their domains. This is especially true for large, sudden spikes in volume, such as a 5x increase during major campaigns like Giving Tuesday.

Concurrent connections: Reduce the number of open connections to Charter.net's MXs.
Messages per connection: Limit the number of messages sent over a single connection.
Messages per minute/hour: Adhere strictly to observed limits. If it's 60-65 per hour, don't exceed that.
Backoff strategy: When a deferral is received, implement a longer backoff period, like one hour, before retrying.

Even with these adjustments, it can take time for Charter.net's systems to recognize the change and ease the throttling. The goal is to demonstrate consistent, non-abusive sending behavior over an extended period. For more details on adapting to various ISP rules, consider reading about preventing throttling from other email clients.

Advanced considerations and long-term strategy

If you're using a specific SMTP MAILFROM domain that might be shared or has historical issues, changing it can offer a temporary reprieve. However, this is often a short-term solution, as new domains or IPs can eventually face similar throttling if the underlying sending behavior or content remains unchanged. It is not ideal to change this for only one provider, especially if Charter.net represents a small percentage of your overall volume.

Contacting Charter.net's postmaster

Attempting to contact Charter.net's postmaster team (e.g., via unblock@charter.net) for direct assistance often yields no response. This is a common complaint among senders, making proactive adjustments to your sending infrastructure and strategy even more critical. Information on how to contact them is limited and often outdated.

In the long term, focus on building and maintaining a strong sender reputation across all ISPs. This involves consistent email engagement, meticulous list hygiene, and adherence to email sending best practices. Continuous monitoring of your deliverability, including bounce rates and reputation metrics from various sources, will help you identify and address issues before they escalate into severe throttling or blocklist (or blacklist) placements. Regular blocklist monitoring can help catch problems early.

Views from the trenches

Best practices

Implement granular rate limiting and connection management specifically for Charter.net domains, not just overall volume.

Segment your Charter.net audience to prioritize highly engaged recipients for critical campaigns like Giving Tuesday.

Common pitfalls

Assuming overall good reputation with other ISPs translates directly to Charter.net's acceptance policies.

Ignoring

Expert tips

Consider a separate IP pool or sending service for Charter.net if their throttling remains persistent and impacts crucial volumes.

Analyze Charter.net's postmaster error logs thoroughly to understand specific rejection reasons beyond generic throttling.

Expert view

Expert from Email Geeks says that throttling is often reputation-based, related to the number of concurrent or total connections opened.

2023-11-29 - Email Geeks

Marketer view

Marketer from Email Geeks says that if Charter is only allowing one message per minute, it indicates a serious reputation issue from their perspective.

2023-11-29 - Email Geeks

Navigating Spectrum's email landscape

Resolving email throttling issues with Charter.net, or Spectrum, boils down to a fundamental principle: adapting your sending practices to their specific requirements, rather than assuming universal deliverability standards. Even with excellent overall sender reputation and proper email authentication, Charter's nuanced filtering systems can impose limitations, particularly on high-volume senders.

By understanding the difference between rate and concurrency limits, implementing precise sending controls, and committing to a long-term strategy of gradual volume increase and continuous monitoring, you can mitigate throttling. While direct communication with their postmaster might be challenging, consistent adherence to adapted sending rules will ultimately improve your deliverability to Charter.net recipients.