Why are there connection timeouts to AT&T domains?

Key findings

• Sporadic delivery: Mail may still flow but at a significantly slower and more inconsistent pace.
• Diagnostic errors: Tools like MXToolbox or DNSChecker may report Connection timed out or Connect failed for AT&T mail hosts.
• Ping failures: Attempts to ping affected mail server IPs may result in 100% packet loss, indicating network inaccessibility.
• General issue: Timeouts are often widespread, affecting many senders, suggesting an issue on AT&T's network rather than a specific sender's setup.
• Queue buildup: Outgoing mail queues can grow significantly due to slow connections to AT&T domains.
• Temporary nature: Such issues are often transient, resolving within hours or days, as the ISP addresses the underlying problem.

Key considerations

• Monitor delivery logs: Regularly check your SMTP logs for recurring timeout errors to AT&T domains.
• Check network status: Consult AT&T's support pages or service status updates for known outages or network congestion.
• Leverage diagnostic tools: Utilize online tools for ping and connectivity tests to verify host reachability.
• Understand impact: Recognize that while emails might eventually deliver, consistent timeouts can impact sender reputation.
• Patience: Often, these issues are beyond your control and resolve when the ISP addresses its network problems.

Key opinions

• Widespread reports: Many marketers report similar connection timeout issues to AT&T domains, indicating a broader problem.
• Verification methods: Confirming timeouts with tools like MXToolbox or DNSChecker helps validate the issue.
• Delayed delivery: Despite timeouts, mail often eventually gets delivered, though significantly delayed and sporadically.
• Queue accumulation: Marketers observe their email queues building up due to slow or failed connections to AT&T servers.
• Network speculation: Common theories for timeouts include the receiving server being overwhelmed or under a DDoS attack.

Key considerations

• Impact on campaigns: Be aware that delivery delays can affect the timing and effectiveness of email campaigns.
• Sender reputation: While often not a direct blacklist issue, persistent timeouts can subtly harm reputation.
• Monitor internal metrics: Keep a close eye on your own email logs and queue sizes to track the severity of the problem.
• Communicate internally: Inform relevant teams about ongoing delivery issues to AT&T domains.
• Review AT&T policies: Familiarize yourself with AT&T email policies to ensure compliance, even during network disruptions.
• Check for blacklistings: Verify if your IP is on an AT&T blacklist or any other major blocklist that might cause issues.

Key opinions

• Network diagnosis: Experts advise attempting manual connections to affected mail hosts to verify reachability.
• Scope of issue: If multiple senders experience similar timeouts, it points to a general ISP network problem.
• Packet loss: Ping tests revealing 100% packet loss to mail servers confirm network inaccessibility.
• Root causes: Suspected causes for timeouts include overwhelmed servers, network congestion, or DDoS attacks.
• ISP responsibility: These issues are typically resolved by the ISP, indicating the problem is on their end.
• Transient nature: Most network-wide outages are temporary and service eventually normalizes.

Key considerations

• Deep network investigation: Utilize advanced network troubleshooting, including traceroute and MTR, to pinpoint routing issues.
• Monitor global routing: Keep an eye on BGP routing tables and major internet exchange points for anomalies affecting AT&T.
• Server capacity: Consider the possibility of the receiving ISP's mail servers being at capacity during peak times.
• IP reputation: While not the primary cause of timeouts, ensure your sending IP is not on any major blacklist or blocklist.
• ISP communication: If issues persist, consider escalating with the ISP's postmaster team.
• Validate email authentication: Ensure SPF, DKIM, and DMARC are correctly configured, even if timeouts are network-related.

Key findings

• Cabling and modem sync: Connection errors can be caused by physical issues like unplugged cables or modems losing synchronization.
• DNS error assist: Certain ISP services, such as AT&T's DNS Error Assist, can interfere with desired network behavior and might need to be disabled.
• Public IP changes: Dynamic IP address changes can sometimes lead to connectivity issues requiring re-evaluation.
• Firewall interference: Local network devices, like firewalls (e.g., pfSense), can block or time out connections to external services, including email servers.
• Content controls: ISP-provided home network management tools (like AT&T Smart Home Manager) can set access rules that inadvertently block or delay connections.

Key considerations

• Local troubleshooting: Before assuming an ISP-wide issue, verify your local network setup, including cables and modem status.
• DNS settings: Investigate if AT&T's DNS Error Assist or similar features are active and potentially contributing to connection problems. See instructions on disabling this.
• Router configuration: Check your router settings for any active content controls or security features that might be inadvertently blocking access to certain domains. AT&T provides guides for managing these.
• Persistent connections: Be aware that applications using persistent HTTP connections might experience issues if routers drop these connections prematurely.
• Security warnings: Review any scam alerts or security advisories related to AT&T domains, as malicious activities can sometimes mimic connection issues.