Summary
Emails are delivered slowly to Comcast on Cyber Monday due to a confluence of factors. High email volumes overwhelm Comcast's servers and lead to deferred mail. Increased spam filtering, traffic shaping, and rate limiting further contribute. Sender reputation issues, stemming from shared IPs, spam complaints, or poor domain standing, exacerbate the problem. Email content triggering spam filters, inadequate IP warming, and misconfigured or absent email authentication (SPF, DKIM, DMARC) also cause delays. Changes have been made to help, but a backlog is expected.
Key findings
- High Email Volume & Server Load: Increased email traffic overwhelms Comcast's servers, leading to processing delays and deferred mail.
- Aggressive Spam Filtering: Comcast implements stricter spam filtering during peak times, causing delays for legitimate emails.
- Traffic Shaping & Rate Limiting: Comcast uses traffic shaping and rate limiting to manage network congestion and prevent abuse, throttling email delivery.
- Sender Reputation Issues: Shared IP reputation, spam complaints, and poor domain standing negatively impact deliverability.
- Email Content Triggers: Email content triggering spam filters exacerbates the delays, especially when filters are sensitive.
- Inadequate IP Warming: Unwarmed or improperly warmed IPs face greater scrutiny and delays.
- Authentication Problems: Missing or misconfigured email authentication (SPF, DKIM, DMARC) can cause ISPs to flag emails as suspicious.
Key considerations
- Optimize Sending Volume & Timing: Adjust email sending volume and timing to minimize server load, especially during peak periods.
- Improve Sender Reputation: Monitor and improve IP and domain reputation to reduce the likelihood of throttling or blocking.
- Enhance Email Content & Structure: Optimize email content and structure to avoid triggering spam filters.
- Implement Robust Authentication: Ensure proper implementation and configuration of SPF, DKIM, and DMARC records.
- Warm-Up New IPs Gradually: Gradually warm up new IP addresses to establish a positive sending reputation.
- Monitor Delivery Rates: Continuously monitor delivery rates to Comcast and other ISPs to identify and address issues proactively.
What email marketers say
9 marketer opinions
On Cyber Monday, emails may be delivered slowly to Comcast due to a combination of factors. These include increased spam filtering, high email volumes straining servers, issues related to shared IP reputation, throttling by ISPs, server overload, email content triggering spam filters, inadequate IP warming, and missing email authentication protocols (SPF, DKIM, DMARC).
Key opinions
- Increased Spam Filtering: Comcast's spam filters may be more aggressive during peak times, causing delays for legitimate emails.
- High Email Volume: The sheer volume of emails sent on Cyber Monday can overload servers, leading to processing delays.
- Shared IP Reputation: Using a shared IP address can lead to deliverability issues if other senders negatively impact the IP's reputation.
- ISP Throttling: ISPs may throttle email traffic based on sender reputation or content, particularly during high-traffic events.
- Server Overload: Increased server load on Comcast's end can cause delays in processing and delivering emails.
- Content Triggers: Email content that triggers spam filters can result in delays, especially with heightened sensitivity during peak times.
- Inadequate IP Warming: New or unproven IPs that aren't properly warmed up may face delays due to heightened scrutiny.
- Authentication Issues: Lack of proper email authentication (SPF, DKIM, DMARC) can cause ISPs to flag emails as suspicious, leading to delays.
Key considerations
- Monitor IP Reputation: Regularly check your IP reputation to ensure it's not negatively impacting deliverability.
- Optimize Email Content: Review and optimize your email content to avoid triggering spam filters.
- Implement Authentication: Ensure proper email authentication (SPF, DKIM, DMARC) is in place to verify your sending legitimacy.
- Warm-Up New IPs: Gradually warm up new IPs before sending large volumes of email.
- Consider Dedicated IP: If you send high volumes of email, consider using a dedicated IP to manage your reputation more effectively.
- Monitor Delivery Rates: Monitor your delivery rates to Comcast to identify and address potential issues promptly.
Marketer view
Email marketer from GMass suggests that not properly warming up new IPs can cause delivery issues, especially during peak sending times like Cyber Monday. ISPs are more likely to scrutinize emails from new or unproven IPs, resulting in delays.
5 Apr 2024 - GMass
Marketer view
Email marketer from Mailjet shares that email content triggering spam filters can lead to delays, especially when filters are more sensitive due to high email volumes on Cyber Monday.
19 Apr 2024 - Mailjet
What the experts say
4 expert opinions
Emails are being delivered slowly to Comcast on Cyber Monday primarily due to high email volume overwhelming Comcast's servers, leading to delays as the system struggles to process the increased traffic. Deferred mail, where Comcast's servers are temporarily unable to accept messages due to overload or other issues, also contributes to this slowdown. Experts affirm these issues are widespread during peak periods like Cyber Monday.
Key opinions
- High Email Volume: The massive volume of emails on Cyber Monday overwhelms Comcast's servers.
- Server Overload: Comcast's servers are temporarily unable to accept messages due to being overloaded.
- Deferred Mail: Emails are being deferred, meaning the receiving server is temporarily unable to accept them, leading to delays.
- Widespread Issue: Experts confirm seeing the same Comcast delivery issues, indicating a common problem.
Key considerations
- Monitor Sending Volume: Be aware of the impact of large sending volumes, especially during peak periods like Cyber Monday.
- Plan for Delays: Anticipate potential delivery delays during high-traffic times and adjust communication strategies accordingly.
- Server Capacity: Recognize that receiving server capacity can be a limiting factor in email delivery speed.
- Optimize Email Sending: Optimize your email sending practices to reduce the burden on receiving servers (e.g., throttling sending rates, optimizing content).
Expert view
Expert from Spam Resource explains that deferred mail, especially during peak periods, means the receiving server (like Comcast's) is temporarily unable to accept the message, leading to delivery delays. This could be due to overload or other issues on their end.
7 Dec 2021 - Spam Resource
Expert view
Expert from Email Geeks suggests the Comcast delivery delays are due to high mail volume, likening it to 'all lines are busy'.
19 Apr 2024 - Email Geeks
What the documentation says
5 technical articles
Emails may be delivered slowly to Comcast on Cyber Monday due to several technical factors. ISPs like Comcast may implement traffic shaping to manage network congestion, throttling email delivery rates. SMTP servers can use rate limiting to prevent abuse and manage server load. High spam complaint volumes and a poor sending domain reputation can cause ISPs to delay or block emails. A strict DMARC policy, if misconfigured, may also lead to legitimate emails being delayed or blocked, particularly when ISPs are more vigilant during peak traffic.
Key findings
- Traffic Shaping: ISPs like Comcast may use traffic shaping to manage network congestion, throttling email delivery.
- Rate Limiting: SMTP servers implement rate limiting to prevent abuse and manage server load, slowing delivery.
- Spam Complaints: High spam complaint volumes can negatively impact sender reputation and lead to delays.
- Domain Reputation: A poor sending domain reputation can cause delays, especially during high traffic.
- DMARC Policy: A strict and misconfigured DMARC policy may cause legitimate emails to be delayed or blocked.
Key considerations
- Monitor Traffic Shaping: Be aware that ISPs may implement traffic shaping during peak periods.
- Understand Rate Limits: Consider SMTP server rate limits and adjust sending practices accordingly.
- Reduce Spam Complaints: Take steps to minimize spam complaints to improve sender reputation.
- Improve Domain Reputation: Work to improve and maintain a positive sending domain reputation.
- Configure DMARC Properly: Ensure DMARC policies are correctly configured to avoid unintended delivery issues.
Technical article
Documentation from Spamhaus clarifies that ISPs like Comcast may implement traffic shaping during peak periods to manage network congestion, which can throttle email delivery rates and cause delays.
8 Jul 2024 - Spamhaus
Technical article
Documentation from Microsoft states that the reputation of your sending domain is crucial for email delivery. A poor domain reputation can result in delays, especially when ISPs are handling large volumes of email traffic.
3 Jul 2024 - Microsoft
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