Summary
The issue of Comcast customers not receiving password reset emails, despite logs indicating successful delivery, is multifaceted. Content triggers within the emails, such as sensitive information or URL shorteners, can activate spam filters. Beyond content, the reputation of the sending domain (particularly subdomains used for transactional emails) plays a significant role. Comcast's aggressive filtering practices and potential blacklisting issues further complicate matters. Technical configurations like SPF, DKIM, and DMARC, as well as potential greylisting delays, need scrutiny. User-end factors, including full mailboxes or incorrectly configured spam filters, cannot be disregarded. Ultimately, understanding that an SMTP '250 OK' response doesn't guarantee inbox delivery is key. Filtering services influence the final disposition of emails, making reputation management, content optimization, and authentication paramount.
Key findings
- Content-Triggered Filtering: Password reset email content, especially sensitive info and URL shorteners, often triggers spam filters.
- Domain Reputation Impacts: The reputation of the sending domain, especially the subdomain for transactional emails, heavily influences deliverability.
- Aggressive Comcast Filtering: Comcast employs aggressive filtering policies, potentially blocking legitimate emails.
- Non-IP Related Issues: Deliverability problems are often not related to IP issues but rather content, reputation, or configurations.
- Authentication Crucial: Proper SPF, DKIM, and DMARC configuration is crucial for bypassing filters.
- Greylisting Delays: First-time emails may face delays due to greylisting.
- SMTP Acceptance Not Guarantee: SMTP '250 OK' indicates acceptance by the server, but not guaranteed delivery to the inbox.
- Filtering Service Influence: Filtering services, like VadeSecure and Cloudmark, influence the final email disposition.
- User-End Settings Matter: User's own settings, like full inboxes and personal spam filters, block messages
- Feedback Loops Block: Users Marking email as spam result in the ISPs blocking emails.
Key considerations
- Content Review and Optimization: Thoroughly review and optimize email content to minimize false positives from spam filters.
- Domain Reputation Management: Proactively manage and monitor domain and subdomain reputation.
- Authentication Verification: Double-check and verify the correct configuration of SPF, DKIM, and DMARC records.
- Monitor Blacklists: Regularly monitor sending IPs and domains for inclusion on blacklists.
- Educate Users: Educate customers to check spam folders and adjust personal filter settings.
- Warm Up New IPs: Gradually warm up new IP addresses when sending from them.
- Test Email Subdomains: Test Email Subdomains to see if emails get through or if content is the issue
- Monitor Post Acceptance Delivery: Monitor Post Acceptance Delivery to ensure emails get through
What email marketers say
8 marketer opinions
Comcast customers not receiving password reset emails, despite logs showing successful delivery, can be attributed to various factors. These range from potential delays due to greylisting, content filtering issues, user-end settings (such as full mailboxes or spam filters), to server-side problems like blacklisting or aggressive filtering by Comcast. Misconfiguration of SPF/DKIM records, domain reputation issues, and negative feedback loops from users marking emails as spam can also contribute to this problem. Ultimately, troubleshooting requires examining content, configurations, and reputation, as well as user-end settings.
Key opinions
- Greylisting Delays: First-time emails to Comcast may experience delays due to greylisting.
- Content Filtering: Password reset email content might trigger spam filters due to certain keywords or URL shorteners.
- User-End Settings: Users' mailbox settings (full mailbox, spam filters) can block emails.
- Blacklisting Issues: Comcast's mail servers might have blacklisting problems, blocking legitimate emails.
- SPF/DKIM Misconfiguration: Incorrect SPF/DKIM settings can cause Comcast to reject emails.
- Aggressive Filtering: Comcast is known for aggressive filtering, especially on transactional emails.
- Reputation Issues: Domain or subdomain reputation can affect email deliverability.
- Feedback Loops: Users marking emails as spam creates negative feedback, leading to blocking.
Key considerations
- Content Review: Carefully review password reset email content to avoid triggering spam filters.
- User Education: Educate users on checking spam folders and adjusting email filter settings.
- Blacklist Monitoring: Regularly monitor sending IPs and domains for blacklisting.
- Authentication Verification: Ensure correct configuration of SPF, DKIM, and DMARC records.
- Reputation Management: Manage and monitor domain and subdomain reputation.
- Feedback Loop Monitoring: Implement feedback loop monitoring and address spam complaints promptly.
- IP Warm-up: Warm up IP addresses gradually when sending from a new IP.
Marketer view
Email marketer from Email Marketing forum explains that if users are marking the messages as spam, that this will create a negative feedback loop that causes Comcast to block the messages.
19 May 2022 - Email Marketing forum
Marketer view
Email marketer from EmailOnAcid Forums points out that Comcast is known for aggressive filtering, particularly on transactional emails. The recommendation is to warm up the IP address gradually when sending from a new IP.
28 Nov 2021 - EmailOnAcid Forums
What the experts say
6 expert opinions
Comcast's issues with password reset email delivery, despite showing successful delivery in logs, appear to stem primarily from content-based filtering and domain reputation, rather than IP-related problems. Experts emphasize that the content of the emails themselves, particularly sensitive information like passwords, can trigger aggressive spam filters. Furthermore, the reputation of the subdomain used for transactional emails can differ from the marketing domain, leading to deliverability issues. Properly configuring email authentication (SPF, DKIM, DMARC) and carefully monitoring sender reputation are also crucial to ensure successful delivery.
Key opinions
- Content Triggers Filters: Password reset emails content, especially when revealing passwords, triggers content and phishing filters.
- Non-IP Related Issue: Comcast's blocking of emails is primarily not IP-related.
- Subdomain Reputation: The subdomain used for transactional emails might have a different reputation than the marketing domain.
- Aggressive Filtering: Comcast uses aggressive filtering policies that can block legitimate emails.
Key considerations
- Content Review and Testing: Carefully review and test the content of password reset emails to avoid triggering spam filters.
- Subdomain Reputation Management: Monitor and manage the reputation of the subdomain used for transactional emails, ensuring consistent sending practices.
- Authentication Setup: Ensure proper setup of SPF, DKIM, and DMARC authentication to improve email deliverability.
- Newsletter List Examination: Examine how the newsletter list is handled, identifying potential triggers for filters.
Expert view
Expert from Email Geeks states that the issue with Comcast blocking marketing emails, even after IP unblocking, is likely not IP-related. Suggests examining how the newsletter list is handled, identifying potential triggers for filters.
7 May 2022 - Email Geeks
Expert view
Expert from Email Geeks suggests the issue isn't related to IPs but rather content or phishing filters. The act of giving out passwords may be triggering a filter.
21 Sep 2023 - Email Geeks
What the documentation says
3 technical articles
Even though SMTP logs show a '250 OK' response, indicating successful acceptance of password reset emails by the receiving server, this doesn't guarantee inbox delivery. Subsequent filtering processes, influenced by threat intelligence from services like VadeSecure and Cloudmark, determine the email's final disposition. These services flag emails with spam or malicious content, which may result in ISPs blocking or quarantining them, despite initial acceptance.
Key findings
- SMTP Acceptance Not Final: SMTP '250 OK' only means acceptance by the server, not guaranteed inbox delivery.
- Filtering Post-Acceptance: Emails undergo further filtering after acceptance, impacting final delivery.
- Threat Intelligence Influence: Services like VadeSecure and Cloudmark influence ISP filtering decisions with threat intelligence.
- Content-Based Blocking: ISPs block or quarantine emails flagged as spam or malicious by filtering services.
Key considerations
- Monitor Post-Acceptance Delivery: Don't rely solely on SMTP logs; monitor post-acceptance delivery metrics.
- Understand Filtering Services: Understand how threat intelligence services used by ISPs filter emails.
- Optimize for Filtering Services: Optimize email content and sending practices to avoid being flagged as spam or malicious.
Technical article
Documentation from VadeSecure explains that while VadeSecure can provide threat intelligence hints to ISPs, the ISP ultimately decides what to do with the email (reject, quarantine, etc.). VadeSecure does not directly provide SMTP reply codes.
16 Apr 2025 - VadeSecure
Technical article
Documentation from RFC Editor explains that SMTP replies, especially '250 OK,' indicate that the mail server has accepted the email for delivery. However, acceptance doesn't guarantee the email will reach the inbox, as further filtering might occur.
8 Jun 2024 - RFC Editor
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