Summary
There has been a notable and widespread increase in email block bounces targeting AT&T domains, affecting numerous senders. This surge isn't isolated to specific platforms or senders with poor reputations; even those with a strong history of good deliverability are experiencing significant rejections.
Key findings
- Widespread Impact: The issue is not confined to a single sending platform but appears to be a global increase in blocks for AT&T domains.
- RBL Listings: Bounce messages frequently indicate listings on a DNSBL (DNS-based blocklist) or RBL (real-time blocklist), often with specific codes like DNSBL:RBL 521.
- US-Based Senders: Many reports suggest this problem is predominantly affecting US-based email campaigns and senders.
- Throttling Ineffective: Simply reducing email volume or throttling sending rates has not proven effective in resolving these blockages.
- Authentication Challenges: While not explicitly stated as the primary cause for the spike, proper email authentication (SPF, DKIM, DMARC) is crucial for avoiding general rejections and can be a factor.
Key considerations
- Review Bounce Messages: Thoroughly examine bounce error codes for any mention of RBLs or specific blocklist names.
- Contact AT&T Support: Reach out to AT&T's abuse contact, often provided within the bounce message itself (e.g., abuse_rbl@abuse-att.net), to inquire about delisting or specific reasons for blocks.
- Monitor Sender Reputation: Proactively monitor your sender reputation, including your IP and domain, across various blocklists and postmaster tools.
- Verify Authentication Records: Ensure your SPF, DKIM, and DMARC records are correctly configured and aligned, as even minor misconfigurations can lead to rejections.
- Address Underlying Issues: If an RBL listing is identified, immediately address the root cause of the listing to prevent recurrence.
What email marketers say
Email marketers across different platforms are reporting a distinct pattern of increased block bounces to AT&T email addresses. This indicates a broader issue affecting the ecosystem rather than isolated incidents.
Key opinions
- Platform Agnostic: The issue is not tied to specific sending platforms, such as Salesforce Marketing Cloud (SFMC), suggesting a broader AT&T-side change.
- Global Phenomenon: There is a consensus among marketers that the increase in AT&T bounces and blocks is a global trend, affecting various clients.
- Specific Bounce Codes: Marketers are observing consistent bounce messages, such as 5.3.0 (unknown mail system-related status) flpd569 DNSBL:RBL 521< ***>_is_blocked.
- Persistent Blocks: Despite attempts to throttle email volume, the blocks appear to be persistent rather than temporary, causing ongoing deliverability challenges.
- Impact on Clean Senders: Even senders with excellent email practices and strong reputations elsewhere are experiencing these unexpected blocks.
Key considerations
- Share Bounce Details: Marketers should share full bounce messages when seeking help, as specific error codes can point to the exact blocklist or reason.
- Check US Campaigns: Pay close attention to deliverability metrics for US-targeted campaigns, as the problem seems more pronounced there.
- Community Engagement: Engage with online communities and forums (like MailOP mailing lists or AT&T's own support forums) to gather more insights and see if collective action or information sharing can help. An example of this can be seen on Constant Contact's community forum.
- Proactive Monitoring: Implement robust monitoring for bounce rates and specific error codes, particularly for major ISPs like AT&T, especially considering what causes a sudden spike in email bounce rates.
Marketer view
Email marketer from Email Geeks inquires whether other users of Salesforce Marketing Cloud are observing a recent increase in block bounces for AT&T email domains. This highlights a concern about potential widespread issues affecting deliverability to a major ISP.
Marketer view
A marketer on the Constant Contact Community forum details that persistent blockages might indicate that a sender has been placed on a specific blocklist. They suggest that examining bounce messages is often the primary method to determine if a listing has occurred, especially for internal or provider-specific blocklists. This approach is crucial for diagnosis when standard checks fail.
What the experts say
Email deliverability experts confirm the recent spike in block bounces to AT&T domains, noting that it impacts even highly reputable senders. They emphasize the need to thoroughly investigate bounce messages for clues regarding the specific blocklists involved.
Key opinions
- Confirmed Spike: Experts are indeed seeing a significant increase in blocks and bounces, affecting clients who are otherwise considered great senders.
- Throttling Insufficient: Adjusting MTA settings to throttle mail volume into AT&T's infrastructure has not appeared to help resolve the issue.
- RBL Identification: For some provider-specific blocklists, examining the bounce message is often the only way to identify if an IP or domain has been listed.
- Sterling Reputation: Many affected senders possess an excellent reputation across nearly all other mailbox providers, making the AT&T issue particularly perplexing. A practical guide to understanding your email domain reputation can help verify this.
- Potential System Changes: The widespread nature of the problem suggests that AT&T may have implemented new security settings or filtering rules, similar to Microsoft 365 email issues.
Key considerations
- Analyze Bounce Headers: Dig deep into the full bounce message headers for specific RBL names or detailed rejection reasons, as these are critical for diagnosis, and to understand how email blacklists actually work.
- Direct Communication: Initiate contact with the abuse email address provided in the bounce message to seek clarification and potential delisting.
- Historical Context: Consider if this situation mirrors past broad blockages by other large ISPs, such as previous Barracuda cases, which often indicate significant system-wide changes.
- Verify All Authentication: Beyond basic presence, ensure that all aspects of SPF, DKIM, and DMARC are correctly configured and pass validation checks to rule out authentication as a contributing factor.
Expert view
An expert from Email Geeks mentions that the issue of high bounces and blocks is not exclusive to SFMC. This expert reports consulting with a client who is a highly reputable sender, yet is experiencing a significant number of rejections despite having already attempted to throttle their email volume at the MTA level. This suggests the problem is more fundamental than simple volume management.
Expert view
An expert from SpamResource often highlights that sudden spikes in rejections by a major ISP like AT&T can indicate a shift in their filtering policies or an increased sensitivity to certain sending patterns. They suggest that even slight deviations from expected norms can trigger new block triggers, requiring senders to adapt their practices.
What the documentation says
Official documentation from AT&T and general email deliverability guidelines shed light on common reasons for email rejections and the mechanisms they employ to filter unwanted mail.
Key findings
- Internal Blocklists: AT&T maintains its own internal blocklists that block emails from senders identified as problematic, as highlighted by MailMonitor's documentation.
- Security Rejections: Emails can be rejected for security reasons if they lack proper authentication (like SPF, DKIM, and DMARC) or if the sending IP/domain is associated with suspicious activity.
- DNSBL/RBL Usage: Bounce messages often explicitly mention DNSBL (DNS-based Blocklist) or RBL (Real-time Blocklist) references when an email is blocked due to a listing.
- Sender Responsibility: Senders are advised to ensure they are not on any blocklists and to identify and fix issues that lead to such listings.
- Recipient-Side Controls: AT&T also provides options for recipients to manage their own blocked addresses and email filters, though this typically pertains to individual user preferences, not bulk rejections.
Key considerations
- Authentication Standards: Adhere strictly to email authentication standards (SPF, DKIM, DMARC) to build and maintain trust with AT&T's mail servers. The recent Yahoo announcement regarding AT&T mail routing underscores the dynamic nature of ISP requirements.
- Abuse Contact: Utilize the abuse_rbl@abuse-att.net email address (or similar official contacts) provided in bounce messages for specific blocklist removal requests.
- Proactive Monitoring: Regularly check your sending IP addresses and domains against major public blocklists and AT&T's specific criteria, if available. AT&T provides general guidance on resolving email issues.
- List Hygiene: Maintain a clean and engaged email list to minimize spam complaints, invalid addresses, and other negative signals that can lead to blocklisting.
Technical article
AT&T Support Community documentation confirms that email servers can be blocked by AT&T's mail servers, with bounce messages often citing 'DNSBL:RBL 521' as a reason for rejection. This indicates that the sending IP or domain has been identified on a blocklist used by AT&T's systems.
Technical article
MailMonitor, in its overview of AT&T's email service, specifies that AT&T maintains a blocklist for preventing unwanted emails. This documentation implies that senders should take responsibility for identifying the cause of any blocklisting and promptly resolve the underlying issue to regain deliverability. Active management of sender reputation is key.
Related resources
6 resources
Related pages
What is a bounce domain and how does its reputation impact email deliverability?
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How to resolve 'Blacklisted by Internal Reputation Service' email bounces from small ISPs?
What causes a sudden spike in email bounce rates, especially from Gmail?
How do email soft bounce retry policies affect domain reputation and deliverability?
Yahoo announces changes to AT&T mail routing
An in-depth guide to email blocklists
What is a DNSBL and how does it affect email deliverability?
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A practical guide to understanding your email domain reputation
