The evidence suggests that BT's (btinternet.com) DMARC policy enforcement is not entirely consistent. While BT's documentation implies engagement with DMARC and prioritizes sender authentication and reputation, tests show mixed results: bt.com accepted DMARC failing mail, whereas btinternet.com blocked mail due to SPF/DKIM failures, not necessarily DMARC. Various factors contribute to this inconsistency, including variations in how ISPs interpret DMARC policies, potential technical limitations, outdated email systems, DNS propagation issues, and the fact that receivers ultimately decide how to handle authentication failures, per DMARC.org and RFC specifications. Correct DMARC setup is vital, but constant monitoring of DMARC reports is equally critical to understand how BT is handling emails failing DMARC checks, and to be aware of potential implementation issues.

The enforcement of DMARC policies by BT (btinternet.com) is inconsistent. Some reports suggest BT may not strictly adhere to DMARC, especially quarantine or reject settings. The interpretation of DMARC policies varies among email providers; some might send emails to spam, while others block them. DMARC reports are crucial for understanding how different ISPs handle DMARC failures, providing insight into BT's practices. Correctly configured DMARC records are essential, with potential rejections if not set up correctly. Older email systems might not fully support DMARC. Inconsistencies in DMARC implementation and DNS propagation can also affect policy application. Therefore, vigilance and monitoring are needed to ensure effective email delivery.

Tests on BT's domains (bt.com and btinternet.com) yield mixed results. bt.com accepted DMARC failing mail. However, btinternet.com blocked mail due to SPF failure and lack of DKIM, not directly due to DMARC. DMARC enforcement is complex and varies among providers, influenced by technical limitations. Simply setting up DMARC is insufficient; monitoring message handling is critical. Moving to a 'p=reject' policy is advisable to potentially improve spam filtering.

BT's documentation implies engagement with DMARC policies to manage spam and phishing, without explicitly stating full adherence. DMARC.org highlights that receivers ultimately decide how to handle authentication failures. RFC 7489 specifies receivers *should* follow DMARC, but exceptions exist. The UK NCSC notes potential inconsistencies in DMARC application among providers. Therefore, while DMARC provides a framework, consistent enforcement cannot be guaranteed.