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Email statuses and errors - types and explanations

In the article, we'll introduce you to the types of statuses and errors you might get when trying to send an email to a specific recipient. The status and error types for each mail server are the same, but each mail server can use a different explanation (text) for them.

101 (Can not open connection) - Most likely, the mail server or mail program can not perform an SMTP session. Possible errors are SMTP Error 101, Error opening connection or SMTP Error 101, can not open SMTP stream. There is probably a server name error, the wrong IP address, or a wrong port in the mail client you are using.

111 (Connection refused) - exhibits when mail client can not connect to the recipient's mail server and the most likely reason for this is wrong configured firewall or wrong domain name. A typical message in this case is this: Connection refused, 111 Can not open SMTP stream.

211 (System Status message or System Help Reply) - The mail server is mostly used to provide help information/commands that allow it to run.

214 (Help Reply message) - Similarly to 211 (System Status message or System Help Reply), information is displayed most often when the HELP command is sent to the mail server.

220 (<ServerName> service is running) - Informs that the mail server is working correctly. The implementation of one of them may provide you with an informational message that you are ready to use the mail server you have contacted.

221 (The domain service is closing the transmission channel) - Data status that says that mail server is processed submitted requests and it closes relationship between the two sides until you get a new request for communication. A common message is 221 Goodbye or 221 Closing connection and 221 Thank you for your business or 221 All messages processed successfully in this session.

250 (Requested mail action OK completed) - Information status that shares the message received and processed.

251 (User not local will forward) - Informs that a message will be forwarded to the required remote mail server.

252 (Can not VRFY (verify) the user - the server will accept the message and will try to deliver it) - This occurs in a very private case where the mail server is divided into separate components that are on different physical servers.

354 (Start mail input end with <CRLF>.<CRLF>,or as a less cryptic description FROM and TO information received, now please provide message body and mark its end with <CRLF>.<CRLF>) - The mail server informs you that it has received information from who and for whom the email is, but also needs the message body of the email so that it can process it.

420 (Timeout communication problem encountered during transmission) - Very rare error, which in many cases means that there is a physical problem with Internet connectivity.

421 (<Servername> Service not available) - The most common reason for such an error is restarting the mail server or overloading a huge email communication. A typical message is this case is 421 Too many concurrent SMTP connections from this IP address; please try again later.

422 (The recipient's mailbox is over its storage limit) - This error indicates that the mailbox or the domain itself has exceeded the allowed quota. You need to increase the quota or delete unnecessary files/emails.

431 (The recipient's mails server is experiencing a Disk Full condition) - This error informs you that the mail server has no free disk space or that the RAM memory is depleted.

432 (The recipient's Exchange Server incoming mail queue has been stopped) - This error is unique for Microsoft Exchange Server and indicates that the mail server is temporarily stopped by an administrator, most likely to fix another problem.

441 (The recipient's server is not responding) - The error indicates that your mail server can not access the other mail server. It will try to connect while sending your email.

442 (Your connection was dropped during transmission) - Your email has been marked for sending, but the process itself has failed to complete successfully. The most likely reason for this is a network problem.

446 (The maximum hop count was exceeded for the message) - The most likely cause is a network problem that revolves your email in a circle and can not reach the destination you need.

447 (Your outgoing message timed out) - The other server does not accept your email and the most common reason is the multiple recipients you have specified.

449 (Routing error) - Error only from Microsoft Exchange Server. In most cases, this is the result of a network problem.

450 Required action not taken - The mailbox was unavailable at the remote end - The backup server does not accept your email. Possible reasons for this may be: the server is stopped, the mailbox has a problem, or the mail server does not accept the email because the sender is blacklisted. Example message 450 Please try again later.

451 (Requested action delayed - Local problem) - Received if your Internet provider or one of the mail servers is experiencing an overload on the service. Typical errors: SMTP error 451 Unable to complete command, DNS not available or timedout __ or 451 Temporary local problem - please try later.

452 (Requested action not taken - Insufficient storage) - Error is indicating that the free disk space on the mail server is critical low. Possible message: 452 Out of memory.

471 (Please try again later) - Most often this error occurs because of the anti-virus or anti-spam filter on the mail server.

500 (Syntax error command not recognized - The mail client you use is most likely to send the wrong SMTP commands to the mail server and it can not process them. Possible message: 500 unrecognized command.

501 (Syntax error in parameters or arguments) - The mail client has submitted a correct command to the mail server, but the parameters are wrong. Example message: 501 5.5.4 Invalid Address.

502 (Command not implemented) - The mail client sends a command to the mail server, which it does not implement.

503 (This mail server requires authentication) - The commands the mail client submitted to the mail server are in а wrong order and are not following the SMTP specification.

504 (Command parameter not implemented) - The mail client has submitted a correct command to the mail server, but the parameters are wrong.

510/511 (Bad Email Address) - The most likely reason is a wrong email address.

512 (DNS error) - The error informs that the mail server can not resolve correctly the domain from which the email was sent or to which it is sending the email.

513 (Relaying denied or Authentication required) - Typically used if the recipient's address is not written correctly in the mail client, most often if it is enclosed in quotation marks. Typical message: 553 5.1.3 User address required! or SMTP error 501 5.1.3 Bad recipient address syntax.

523 (The Recipient's mailbox cannot receive messages this big) - The error is displayed if the email and attachments exceed the allowed size of an email on the server. Typical message: SMTP Error 552 5.2.3 Message exceeds maximum fixed size.

530 (Your server has been blacklisted by the recipient's server) - One of the most common mistakes you can get because it is mostly used if the mail server is blacklisted.

541 (Recipient Address Rejected) - Full Error equivalent 530 (Your server has been blacklisted by the recipient's server). Typical message: SMTP error from remote mail server - 550 5.4.1 Recipient address rejected.

550 (Requested actions not taken as the mailbox is unavailable) - The causes for the error are two: either the firewall of the mail server that sent the email, blocked it, or there is no such mailbox. Typical message: 550 No such user here.

552 (Size of the incoming message exceeds the incoming size limit) - The user has reached a certain limit on the mail server and is not allowed to send more email messages.

553 (Requested action not taken -- Mailbox name invalid) - The error can occur if the recipient's email is misspelled or the PTR (reverse DNS) mail server record is incorrect.

554 (Transaction failed) - The error can occur for many reasons, but the most common is the blacklisting of the sender.

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