Why are emails being delivered slowly to Comcast on Cyber Monday?
Summary
What email marketers say9Marketer opinions
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.
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.
Email marketer from Litmus explains that ISPs sometimes throttle email traffic based on sender reputation or content, and this throttling can be more aggressive during high-traffic events like Cyber Monday, leading to delays.
Marketer from Email Geeks indicates that changes have been made which are helping with the issue, but a backlog is expected.
Email marketer from EmailVendorSelection shares that if you're using a shared IP address for sending emails, the reputation of that IP can be affected by other senders, leading to deliverability issues and delays, especially during high-volume periods like Cyber Monday.
Email marketer from MarketingProfs explains that high email volumes on Cyber Monday strain email servers, leading to processing delays and slower delivery times across all ISPs, including Comcast.
Email marketer from Reddit suggests that Comcast's slow email delivery on Cyber Monday could be due to increased spam filtering during peak traffic times, causing delays for legitimate emails as well.
Email marketer from Quora suggests that lack of proper email authentication (SPF, DKIM, DMARC) can lead to delivery delays as ISPs may flag unauthenticated emails as suspicious during high-volume periods.
Email marketer from StackOverflow suggests that increased server load on Comcast's end during Cyber Monday can cause delays in processing and delivering emails to users.
What the experts say4Expert opinions
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.
Expert from Email Geeks suggests the Comcast delivery delays are due to high mail volume, likening it to 'all lines are busy'.
Expert from Word to the Wise highlights that the sheer volume of email sent during Black Friday and Cyber Monday can overwhelm receiving servers, leading to delays. Even legitimate senders may experience slower delivery due to the overall increase in traffic.
Expert from Email Geeks responds to the original question with a simple affirmation that they are also seeing the same Comcast delivery issues.
What the documentation says5Technical articles
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.
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.
Documentation from Google Postmaster Tools explains that a high volume of spam complaints can negatively impact sender reputation and cause ISPs to delay or block email delivery.
Documentation from DMARC.org clarifies that having a strict DMARC policy (e.g., p=reject) without proper configuration can cause legitimate emails to be delayed or blocked, especially during peak traffic when ISPs are more vigilant.
Documentation from RFC 5321 specifies that SMTP servers can implement rate limiting to prevent abuse and manage server load, which can result in slower email delivery, particularly during peak sending times.