How to parse SMTP responses to identify hard and soft bounces?

Email marketer from authsmtp.com explains that interpreting bounce emails requires parsing the SMTP response code within the email body. Different mail servers produce different output, however almost all will include the important SMTP response.

Marketer from Email Geeks suggests separating 5xx from 4xx response codes and manually reviewing what is happening, sorting by receiver (e.g., Yahoo 5xx, Yahoo 4xx). He cautions that not all 5xx errors are permanent errors.

Email marketer from mailtrap.io explains that hard bounces occur when the email address is invalid or does not exist. These typically result in a 5xx SMTP error code, signaling a permanent delivery failure. Identifying these is crucial for maintaining a clean email list.

Email marketer from emailonacid.com, explains that effective bounce management requires parsing SMTP responses, categorizing bounces, and automatically removing hard bounces from your email list to maintain sender reputation.

Email marketer from sendgrid.com shares that soft bounces are temporary delivery failures, often due to a full inbox or server issues. They usually return a 4xx SMTP error code. Repeated soft bounces should be treated with caution as they can turn into hard bounces.

Marketer from Email Geeks explains that any 5xx response code should technically be considered a hard bounce. However, it's often more nuanced, and some 4xx responses (e.g., server busy) are effectively hard bounces. Suggests considering repeated 4xx responses as hard bounces.

Email marketer from stackoverflow.com responds that using regular expressions to parse SMTP replies is a common approach. They recommends focusing on extracting the three-digit code and any associated text message for detailed analysis.

Email marketer from litmus.com explains that high bounce rates negatively impact sender reputation, leading to deliverability issues. Properly parsing SMTP responses and managing bounces is crucial for maintaining a healthy email program.

Email marketer from reddit.com shares that a good starting regex pattern is `^\d{3}[\s\-]+(.*)$` which captures the status code and message. Further refinement is needed based on specific server responses.

Email marketer from elasticemail.com recommends that you should set up automated bounce processing to filter hard bounces from your system and remove the addresses. This will improve deliverability and keep costs down as you aren't sending emails to bad addresses.

Email marketer from sparkpost.com shares that interpreting bounce codes involves understanding that 5xx codes indicate permanent errors, while 4xx codes suggest temporary issues. The specific digits provide more granular information, like mailbox full or user unknown.

Expert from Word to the Wise explains that accurately categorizing bounces requires a nuanced approach beyond simple 4xx/5xx codes. It involves considering the specific wording of the SMTP response and implementing custom logic to handle variations across different mail servers.

Expert from Spam Resource recommends using advanced parsing techniques, including regular expressions and natural language processing, to accurately interpret SMTP responses and identify the underlying reasons for bounces. Contextual analysis of the error message is crucial for differentiating between various soft bounce scenarios.

Documentation from exim.org details that bounce processing involves examining the SMTP response codes and messages to categorize bounces. Hard bounces (permanent failures) typically have 5xx codes, while soft bounces (temporary failures) have 4xx codes. Regex patterns are used to match specific error messages for finer-grained classification.

Documentation from mozilla.org outlines that SMTP response codes are three-digit numbers where the first digit signifies the class of response: 2xx (success), 4xx (transient failure), and 5xx (permanent failure). Parsing these codes is the first step in identifying bounce types. Detailed error messages should be analyzed for more specific classifications.

Documentation from microsoft.com details that Non-Delivery Reports (NDRs) in Exchange Server include SMTP response codes that categorize delivery failures. Analyzing these codes is essential for understanding and managing bounced messages.

Documentation from ietf.org explains that SMTP enhanced status codes provide a structured way to determine the outcome of an email delivery attempt. The first digit indicates success, persistent transient failure, or permanent failure. The second digit indicates the subject area, and the third provides detail. Parsing these codes allows for programmatic identification of hard and soft bounces.