Why are Comcast customers not receiving password reset emails despite logs showing successful delivery?
Matthew Whittaker
Co-founder & CTO, Suped
Published 25 Apr 2025
Updated 15 Aug 2025
8 min read
It can be incredibly frustrating to see your email service provider’s logs confirm successful delivery, yet your Comcast (Xfinity) customers insist they haven't received their password reset emails. This isn't an uncommon scenario, and it points to a common misconception in email deliverability: a 250 OK response from the recipient server doesn't always guarantee an email lands in the inbox. It simply means the email was accepted for further processing.
The challenge intensifies when you're dealing with critical transactional emails like password resets, especially when other email types, such as marketing campaigns, are delivering perfectly fine to the same recipients. This discrepancy suggests that the issue isn't necessarily a blanket block on your sending IP or domain.
Many factors can lead to this invisible delivery failure, particularly with large internet service providers (ISPs) like Comcast. It requires a deeper dive into content, authentication, and internal filtering mechanisms that happen post-acceptance.
Content and internal filtering
When password reset emails are not reaching Comcast inboxes despite successful delivery logs, a primary suspect is often the content itself. ISPs, especially for sensitive email types, employ sophisticated content and phishing filters. Even if your marketing emails get through, a password reset email might trigger different, stricter rules. This could be due to specific keywords, link structures, or even the overall tone that an automated system perceives as suspicious.
It’s important to analyze the exact wording, links, and formatting within your password reset emails. Are there any elements that could be mistaken for a phishing attempt, even if benign? Sometimes, simply rephrasing or restructuring the email can make a significant difference. You might consider A/B testing variations of your password reset email content to see if one performs better than another with Comcast recipients.
Another angle to consider is if these emails are being delivered to a specific folder other than the inbox, such as spam or junk. While customers might claim to have checked these folders, sometimes emails can be routed to less obvious locations or simply vanish. Encourage customers to check all possible folders and even search their mailbox for the sender's domain. In some cases, the issue might even be on the recipient's mail client or anti-virus software, not necessarily Comcast's filtering.
Authentication issues
Even if your email logs show a 250 OK response, it's crucial to ensure your email authentication is perfectly configured, especially for transactional sends. DMARC, SPF, and DKIM are fundamental to verifying your email's legitimacy and preventing it from being flagged as spam or spoofed. A misconfiguration, even a subtle one, can lead to silent discarding of emails by major ISPs.
For password reset emails, strong authentication is non-negotiable. If your DMARC policy is set to p=none, you might not be seeing rejection reports, but emails could still be failing DMARC and ending up in spam. Comcast, like other major providers, heavily relies on these authentication protocols.
I recommend double-checking your DMARC, SPF, and DKIM records for your transactional subdomain. Even a single syntax error or an outdated record can cause significant deliverability issues. Ensure that the subdomain used for password resets is properly authenticated. You can use a DMARC record generator to confirm proper setup.
Typical authentication issues
SPF record errors: Exceeding the 10-lookup limit, including incorrect IP addresses, or not having the sender authorized.
DKIM signature problems: Incorrect public key in DNS, a mismatch between signing and verifying headers, or a corrupted signature.
DMARC alignment failures: SPF or DKIM domains not aligning with the From header domain, causing emails to fail DMARC checks. This can lead to DMARC verification failed errors.
Sender reputation and subdomains
Even with perfect authentication and well-crafted content, your sender reputation plays a massive role in deliverability. Although your marketing emails might have a good reputation, a separate subdomain for transactional emails has its own reputation. If this transactional subdomain (or its underlying IPs) has recently experienced issues like sending to stale lists, hitting spam traps, or seeing a sudden spike in volume, its reputation could be negatively impacted specifically with Comcast.
Comcast's filtering systems (which may or may not use third-party blocklists, or their own internal ones) can silently quarantine or drop emails from senders with a questionable reputation. This is where you wouldn't get a bounce message, as the email was accepted, but it never reaches the inbox. It's a form of silent filtering, where the ISP decided the email wasn't wanted after all.
Monitoring your sender reputation, including any associated IPs, is essential. Even if you're not on a public blacklist (or blocklist), private internal blacklists used by ISPs can affect your deliverability. Regularly checking your domain and IP health can help you identify potential issues before they severely impact your email program. Remember, even if you’re using an email service provider, understanding these aspects is critical.
Transactional subdomain
Password reset emails, account notifications, order confirmations.
Recipient expectation: High, immediate need for this email.
Content sensitivity: High, often contains sensitive links or information, subject to strict phishing filters.
Marketing subdomain
Newsletters, promotional offers, product updates.
Recipient expectation: Varies, often lower immediate need.
Content sensitivity: Lower, less likely to trigger security-specific filters.
Engaging with Comcast support
When you're facing consistent deliverability issues with Comcast, despite logs showing acceptance, direct engagement with their support or postmaster team is critical. While it can be challenging to get a response, persistence is key. They are the only ones who can provide definitive reasons for internal filtering that doesn't result in bounces.
When contacting Comcast's delivery support, provide as much detail as possible. This includes specific message IDs, recipient email addresses (with permission), sending IP addresses, timestamps, and the exact SMTP 250 OK reply string you received. Even a successful 250 OK response can sometimes contain an internal ID or further information that helps their team trace the email's path within their system. It's crucial to confirm if your logs are indeed showing the SMTP replies from Comcast and not just internal application logs.
While awaiting a response, you can also investigate potential third-party anti-spam solutions that Comcast might be leveraging. Although they manage their own policy, some ISPs use hints from providers like Vade Secure. Knowing this information can sometimes help you understand the landscape of their filtering, though direct contact with Comcast remains the most effective path for resolution.
Steps to troubleshoot and resolve
To systematically troubleshoot this problem, a multifaceted approach is best. Start by re-evaluating the content of your password reset emails. Simplify the language, reduce unnecessary links, and ensure the call to action is clear and direct. Make sure there are no elements that could be misconstrued as malicious.
Next, rigorously verify your email authentication settings (SPF, DKIM, DMARC) for the sending subdomain. Use a DMARC record generator to ensure everything is correct and that your policies align. If you're not already, consider implementing a DMARC policy that provides reporting (e.g., p=none with rua tags) to gain visibility into your authentication pass/fail rates. These reports, while technical, can provide clues as to why emails are failing even if they're accepted initially.
Finally, monitor your sender reputation closely. While Comcast might not be responding to general unblock requests, maintaining a pristine sending history from that transactional subdomain is paramount. This problem with transactional emails to Comcast is often due to a combination of these factors rather than a single, obvious block.
Views from the trenches
Best practices
Ensure your DMARC, SPF, and DKIM records are perfectly configured for the transactional subdomain.
Simplify the content of password reset emails; remove extraneous links and text.
Encourage affected users to check all mail folders, including spam, junk, and 'other' inboxes.
Contact Comcast's delivery support directly with specific email headers and SMTP logs for affected messages.
Maintain a consistent and clean sending reputation from your transactional domain.
Common pitfalls
Assuming '250 OK' means guaranteed inbox delivery, ignoring post-acceptance filtering.
Focusing solely on IP blacklists when content or authentication might be the issue.
Not differentiating between the reputation and filtering rules for transactional vs. marketing emails.
Failing to provide detailed SMTP replies and message IDs when contacting ISP support.
Ignoring customer reports of non-receipt if logs show successful delivery.
Expert tips
Consider temporarily sending password reset emails from your well-reputed marketing subdomain as a test.
Look for commonalities among the affected Comcast customers, such as email client or AV software.
Check for any external anti-spam solutions that Comcast might be using for filtering hints.
Ensure your transactional sending IP addresses are not listed on any relevant public or private blocklists.
If using a third-party ESP, confirm their understanding of Comcast's unique filtering nuances.
Expert view
Expert from Email Geeks says to investigate the possibility that the content of password reset emails is triggering phishing filters, especially if other emails are delivering successfully.
2023-01-15 - Email Geeks
Marketer view
Marketer from Email Geeks says they would contact Comcast delivery support with specific SMTP logs to get more insight into what's happening post-delivery.
2023-02-20 - Email Geeks
A path to inbox success
Solving the mystery of missing password reset emails to Comcast customers requires a comprehensive and analytical approach. It rarely boils down to a simple, obvious cause. By meticulously examining content, verifying authentication, understanding the nuances of sender reputation (especially for subdomains), and diligently engaging with Comcast's support, you can uncover the root cause and implement lasting solutions.
Remember that a 250 OK from an ISP indicates acceptance, not guaranteed inbox placement. Many factors influence where an email ultimately lands post-acceptance, and staying vigilant on all fronts of your email deliverability strategy is the best way to ensure your critical messages reach their intended recipients.
