Why are Bounceback Message, SMTP Reply Code, and SMTP Error Code fields blank in bounce reporting?

Email marketer from Sendgrid Support explains that some errors can occur if sender lacks proper DNS records. Without these records, a receiving server may not be able to verify the sender's authenticity, leading to rejection without full bounce details.

Email marketer from EmailOctopus Support shares that blank bounce information can indicate the email was blocked before it reached the recipient's server, preventing a standard bounce message. It also explains that auto-responders or vacation replies may not always provide structured SMTP error codes.

Email marketer from Mailchimp Support states that if Mailchimp's system sees a strange SMTP response, then the bounce information may not be correctly parsed and displayed.

Email marketer from Reddit user u/EmailGuru123 explains that blank fields often mean the bounce is asynchronous. The receiving server accepted the email initially but failed to deliver it later, without sending a detailed immediate bounce message.

Email marketer from Stack Overflow user TechUser42 describes that incomplete SMTP responses can occur if the receiving server closes the connection prematurely or doesn't follow the standard SMTP protocol strictly, leading to missing information in the bounce report.

Email marketer from Litmus Support shares that auto-replies and out-of-office messages often lack the structured data needed to populate bounce reporting fields, as they are not intended to be machine-readable.

Email marketer from Mailjet Support details that sometimes the receiving server's configuration prevents sending back detailed SMTP information, resulting in blank fields. They also note that some bounce messages are simply non-standard and lack the expected codes.

Email marketer from Quora user QuoraEmailExpert explains that greylisting (temporary rejection of emails from unknown senders) can sometimes lead to incomplete bounce reports if the sending server doesn't retry delivery as expected.

Email marketer from Email Marketing Forum user MailForumUser discusses that aggressive spam filtering can block emails before they generate a standard bounce, resulting in incomplete bounce data. Internal firewalls might also prevent proper SMTP communication.

Expert from Email Geeks explains that you’d really need to know where those fields come from, and what the raw data behind them is. Unless the raw data is available in your ESP web interface you’d have to ask support for more details about what’s going on.

Expert from Email Geeks shares that their being blank suggests it’s an asynchronous bounce, which absolutely could be caused by elderly autoresponders. If it’s 0.00001% of your list I’d accept that explanation and move on. If it’s 1% I’d want to see the raw data.

Expert from Email Geeks shares that the platform might not be extracting the relevant information from the bounce email to populate their reporting, and that the information should be in the email, but sometimes bounce handlers don't deal with it well.

Expert from Spam Resource shares that diagnostic codes may be missing in bounce reporting because they were never issued in the first place. In some instances, a response code should have been sent but was skipped.

Expert from Email Geeks explains that there are two kinds of delivery failures: "in band" during the SMTP transaction (rejection/bounce) and "out of band" where the receiving mail server accepts the message and then decides AFTER the SMTP transaction that the message cannot be delivered by sending mail to the address in the Return-Path.

Expert from Email Geeks adds that some bulk email sending systems will not attempt to send the message due to internal rules / suppression lists / etc. Sometimes these are not recorded with an SMTP rejection message - as it never got to the SMTP stage.

Expert from Email Geeks responds that if it is autoresponders then you absolutely want to pull them off your list. You do not want to be sending mail into ticketing systems or the like.

Expert from Word to the Wise explains that a missing SMTP code is often the result of a server that is not configured to report the specific code or classify the failure in a standard way. Some servers are also set up to hide detailed error messages.

Documentation from Postfix Documentation explains that the level of detail provided in bounce messages depends on the configuration of the Postfix server and how it is set up to interact with other mail servers. In some cases, detailed error reporting may be disabled for security reasons.

Documentation from Microsoft Learn explains that blank SMTP fields in bounce reporting can occur when the receiving server does not provide detailed error information during the SMTP transaction, or the email was never actually sent to the server due to internal filtering.

Documentation from Amazon SES Documentation explains that some bounces are categorized as 'Undetermined' and may lack detailed information due to the way the receiving server handles the failure or due to internal processing within AWS.

Documentation from RFC Editor explains that while SMTP enhanced status codes are designed to provide more detailed error reporting, their implementation and adherence vary across different mail servers. Some servers may not fully implement or expose these codes, leading to missing information in bounce reports.