What does SMTP deferred message 'refused to talk to me: 421 4.7.0 Not allowed' mean?

Email marketer from Digital Ocean mentions that 421 errors often appear when there are issues with the configuration of your mail server, such as incorrect DNS settings or missing authentication records. They suggest reviewing your setup to ensure it meets best practices.

Marketer from Email Geeks shares that the SMTP deferred message likely indicates a manual IP-based block and suggests contacting the provider or using Mailop.

Email marketer from Email Provider Forum suggests that the '421 4.7.0 Not allowed' error can sometimes be caused by reverse DNS (rDNS) issues or incorrect SPF records. They advise checking these settings to ensure they are properly configured for your domain.

Email marketer from Stack Overflow suggests that this error often means the server you're trying to connect to has blocked your IP address or domain. It advises checking blacklists and ensuring your server is properly configured.

Email marketer from Reddit advises that a 421 error can be triggered by rate limiting on the recipient server, which restricts the number of emails accepted from a particular source within a given timeframe. It suggests waiting and retrying later, or adjusting sending volumes to avoid triggering the limit.

Email marketer from DNSQueries says that the 421 error could be due to problems with your domain's DNS records. Confirm that your MX records, SPF records, and DKIM records are correctly configured.

Email marketer from Reddit shares their experience with GoDaddy, noting that a 421 error could be related to exceeding sending limits or triggering spam filters. They recommend contacting GoDaddy support to investigate further.

Email marketer from Mailjet says this type of error often indicates the recipient's mail server is too busy or unavailable. It advises waiting a short period before attempting to resend the email.

Email marketer from MXToolbox explains that a 421 error indicates a temporary problem and could stem from greylisting, where the receiving server temporarily rejects the email to combat spam. Retrying the email later is advised.

Email marketer from Super User highlights that the 421 error might occur if a firewall is blocking the SMTP server's connection. Check your firewall settings to ensure they are not interfering with email traffic.

Expert from Spamresource explains that a 421 error can occur due to greylisting techniques employed by receiving mail servers as a method to combat spam. The server temporarily rejects emails from unknown senders, with the expectation that legitimate senders will retry sending the email later.

Expert from Word to the Wise explains that a 421 SMTP error can indicate several temporary server issues, including server overload, maintenance, or anti-spam measures. It emphasizes that retry attempts are crucial, but persistent 421 errors may suggest underlying configuration problems that need investigation.

Documentation from cPanel Documentation explains that a 421 SMTP error signifies that the service is temporarily unavailable and suggests that the sending server should try again later. It could be due to server overload, maintenance, or temporary blocking policies.

Documentation from Microsoft Docs explains that a 421 error, including variations like '4.7.0 Not allowed', generally signifies 'Service not available, closing transmission channel'. This can indicate a temporary issue on the server side, such as being overloaded or undergoing maintenance.

Documentation from Oracle Help Center mentions that this error code signifies a transient negative completion reply. It means the command was not accepted and the transaction failed, but the error is temporary and the request might succeed if retried.

Documentation from RFC 5321 details SMTP reply codes, explaining that a 421 code signifies that the service is not available. The server knows that it is unable to provide the service. A later retry may be successful.