What causes Comcast email throttling and how can I improve my open rates?
Summary
What email marketers say12Marketer opinions
Email marketer from EmailToolTester suggests that volume limits depend on your sender reputation, and whether your IP address is new. Start by warming up your IP and keep the volume low to help.
Email marketer from Litmus explains the importance of A/B testing subject lines to determine which ones resonate most with your audience. They suggest testing different wording, emojis, and personalization techniques to maximize open rates.
Email marketer from Sendinblue recommends actively managing your sender reputation by monitoring blocklists, promptly addressing spam complaints, and ensuring your domain and IP addresses are properly authenticated with SPF, DKIM, and DMARC records to avoid throttling.
Marketer from Email Geeks refers to a Rate Limit (RL) code and explains that the throttling is due to an internal reputation system based on historical quantity and quality. They indicate that spam reports negatively affect this reputation.
Email marketer from HubSpot shares that cleaning your email list regularly by removing inactive or unengaged subscribers improves deliverability and open rates by sending to an audience that's genuinely interested in your content.
Email marketer from SparkPost emphasizes the importance of maintaining a clean email list to avoid spam complaints, which significantly impact sender reputation and lead to throttling. SparkPost advises regularly cleaning lists, using double opt-in, and providing easy unsubscribe options.
Email marketer from Reddit says, 'I used to have this problem. Make sure you're authenticated properly (SPF, DKIM, DMARC) - that helped me a lot!'
Marketer from Email Geeks explains that a poor open rate is caused by emails being marked as spam.
Email marketer from Reddit explains that improving open rates requires compelling subject lines and preheader text that accurately reflects the email's content and create a sense of urgency or curiosity.
Email marketer from Neil Patel's Blog recommends segmenting your email list to send targeted content, personalizing emails with recipient names, and testing different send times to find optimal engagement windows to improve open rates.
Email marketer from Mailchimp shares that consistent sending schedules build trust with ISPs and improve deliverability, which indirectly boosts open rates. They recommend setting a predictable cadence and sticking to it.
Email marketer from Mailjet explains that Comcast throttling often stems from sending too many emails too quickly, especially from new IPs. Mailjet recommends warming up your IP gradually, monitoring sender reputation, and ensuring recipients are genuinely opted-in.
What the experts say4Expert opinions
Expert from Word to the Wise shares that improving engagement, particularly email opens and clicks, depends on list management (clean lists, opt-in processes) and relevant, personalized content to make sure people are opening and clicking your emails.
Expert from Spam Resource explains that throttling usually means you are sending too fast or have a poor reputation. Laura Atkins recommends focusing on sender reputation and authentication.
Expert from Email Geeks explains that being 'throttled' generally means you’re sending too fast and suggests slowing down, especially with a new subdomain.
Expert from Word to the Wise indicates that Comcast throttling can be due to volume and reputation. They recommend warming up IPs slowly and monitoring feedback loops.
What the documentation says3Technical articles
Documentation from RFC Editor explains that 4xx SMTP codes indicate a transient failure. It could be a temporary issue or the server is declining to send the message. If the client retries later, they might succeed.
Documentation from Comcast Postmaster Site explains that throttling (421 error codes) typically indicates a temporary condition where Comcast's servers are too busy or the sender's email practices trigger rate limiting. Possible causes include high sending volume from a new IP/domain, poor sender reputation, or spam complaints.
Documentation from Microsoft details how they use sender reputation as a major factor in filtering email. Microsoft will analyse an IPs reputation based on spam complaints and other factors to block emails.