What does Apple bounce code CS01 mean and how does email forwarding affect it?

Email marketer from ReturnPath (now Validity) explains how forwarded emails often fail SPF checks because the original sender's SPF record does not authorize the forwarding server. SRS can mitigate this by rewriting the sender address.

Email marketer from Postmark explains that forwarding emails without proper SPF and DKIM handling can lead to deliverability issues, including bounces. When an email is forwarded, the original SPF record might no longer be valid, leading to the email being flagged as spam.

Email marketer from Reddit says that CS01 is likely triggered when a forwarded email fails DMARC checks because the forwarding server isn't authorized to send on behalf of the original sender's domain. If Apple's mail server is set to reject emails that fail DMARC, this would result in the bounce.

Email marketer from SocketLabs suggests that a 'Message rejected due to local policy' (CS01) typically means that the recipient's mail server has a rule or filter that your message triggered. Forwarding could lead to authentication failures, causing the forwarded email to look suspicious.

Email marketer from EmailonAcid suggests that a CS01 error could be triggered if a forwarded email fails SPF or DKIM authentication. Implementing SRS (Sender Rewriting Scheme) is crucial for maintaining deliverability when forwarding emails.

Email marketer from Mailhardener states that bounce code CS01 usually stands for 'Message rejected due to local policy', which indicates an issue with the recipient's mail server policies and potentially relates to spam detection. Email forwarding can exacerbate the issue if SPF or DKIM records are not properly configured to handle the forwarding.

Marketer from Email Geeks explains that if the email was auto-forwarded it likely broke DKIM/SPF, which caused the bounce.

Email marketer from EmailDeliveryGuru.com shares that CS01 errors often relate to spam filtering policies on the recipient's (Apple's) end, and that forwarding can trigger these filters if the forwarded message fails authentication checks (SPF, DKIM).

Marketer from Email Geeks shares that they have issues with the forwarder too.

Email marketer from StackExchange says that email forwarding can alter the email headers and break SPF records, particularly if the forwarder doesn't use SRS (Sender Rewriting Scheme). This can cause receiving mail servers to flag the email as potentially spam.

Marketer from Email Geeks explains that the bounce message (mailer-daemon) would be generated by the forwarder.

Email marketer from MXToolbox says CS01 message rejection due to local policy, can be caused by forwarding if the SPF record of the original domain is not set up to allow the forwarding server to send emails on its behalf. This causes the forwarded email to fail authentication checks.

Expert from Email Geeks explains that it might just be that forwarder forwards lots of spam and is blocked.

Expert from Email Geeks explains that CS01 is specifically a spam block and suggests it's likely forwarding.

Expert from Word to the Wise explains that email forwarding can negatively impact deliverability due to broken authentication. When an email is forwarded, SPF and DKIM records may fail, causing receiving mail servers to flag the email as spam. This can lead to bounces and delivery issues, particularly if Apple's mail server has strict spam filtering policies.

Expert from Spam Resource explains that the Apple CS01 error code signifies a rejection due to local policy, often related to spam filtering. They suggest that email forwarding can exacerbate this issue if SPF and DKIM records are not properly configured, causing the forwarded message to appear as spam. They recommend ensuring proper email authentication setup to avoid being flagged by Apple's servers.

Documentation from Apple Support explains that they provide general information about bounce messages, but does not specifically list error code CS01. Suggests contacting the email provider for specific details.

Documentation from Microsoft says that NDRs with codes like 5.7.1 often indicate policy violations. While they don't specifically mention CS01, the general explanation is that the recipient server's policies are rejecting the email. Forwarding can complicate authentication and trigger these policies.

Documentation from RFC-Editor.org describes 5.7.1 as 'Delivery not authorized, message refused'. Further interpretation needs to be provided by the receiving mail system.

Documentation from DMARC.org describes that email forwarding often breaks DMARC authentication because the forwarder is not authorized to send on behalf of the original sender's domain. This can result in email being rejected by receiving servers.