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This is a list of Simple Mail Transfer Protocol (SMTP) response status codes. Status codes are issued by a server in response to a client's request made to the server. Unless otherwise stated, all status codes described here is part of the current SMTP standard, RFC 5321. The message phrases shown are typical, but any human-readable alternative ...
This class of status code indicates the client must take additional action to complete the request. Many of these status codes are used in URL redirection. [2]A user agent may carry out the additional action with no user interaction only if the method used in the second request is GET or HEAD.
The current SMTP specification (RFC 5321) clearly states that "the SMTP client retains responsibility for delivery of that message" (section 4.2.5) and "mail that cannot be transmitted immediately MUST be queued and periodically retried by the sender." (section 4.5.4.1). Most MTAs will therefore queue and retry messages, but a small number do not.
Although the SMTP is a mature technology, counting more than thirty years, its architecture is increasingly strained by both normal and unsolicited load. [2] The email systems have been enhanced with reputation systems tied to the actual sender of the email, with the idea of recipient's email servers rejecting the email when a forged sender is used in the protocol.
If your third-party email app is having issues connecting, sending, or receiving emails, you may need to reconfigure your account or update the app. Use these steps to identify and fix the source of the problem.
When you get a message from a "MAILER-DAEMON" or a "Mail Delivery Subsystem" with a subject similar to "Failed Delivery," this means that an email you sent was undeliverable and has been bounced back to you.
Sender Policy Framework (SPF) is an email authentication method which ensures the sending mail server is authorized to originate mail from the email sender's domain. [1] [2] This authentication only applies to the email sender listed in the "envelope from" field during the initial SMTP connection.
If you're having problems sending mail, there are a few troubleshooting steps you can take to fix the problem. Restart your computer:. If you haven't shut down your computer in a while, we recommend that you begin troubleshooting by restarting your computer.