What is SMTP?
SMTP stands for Simple Mail Transfer Protocol. This document provides the brief explanation about SMTP reply codes.
SMTP Error 101 : Cannot open connection
Typically your SMTP server or email program is unable to even start an SMTP session. Possible causes may be : incorrectly spelt SMTP server, invalid IP address, invalid SMTP port or some other process is already using the default SMTP port, port 25.
e.g. "SMTP Error 101, Error opening connection" -or- "SMTP Error 101, cannot open SMTP stream"
SMTP Error 211 : System Status message or System Help Reply
SMTP status 211 prefaces a message about the Mail Server status. You might for example issue a command to the mail server to display a list of commands you can use and the server replies with an SMTP Reply 211 followed by the list you requested.
SMTP Error 214 : Help Reply message
SMTP status 214 is usually in reply to the "HELP" command. It displays information about the server, usually a URL to the FAQ page of the SMTP software running on the server.
SMTP Status 220 : <Server Name> service is running
This is normally the first message you will get back from the server. It means the mail service is running . It will normally contain a welcome message and/or the title of the SMTP software and, sometimes, the version number of the mail server software.
SMTP Error 221 : The domain service is closing the transmission channel
The server is ending the mail session – it is closing the conversation with the ISP as it has no more mail to send in this sending session.
e.g. "221 Closing connection" -or- "221 Goodbye"
SMTP Status 250 : Requested mail action OK completed
The mail server has successfully delivered the message! This is the best SMTP reply to receive - your message has been accepted and transmitted OK !
SMTP Status 251 : User not local will forward to <forward-path>
The email account is not local to the ISP server but the ISP server will accept the email and will forward it.
SMTP Status 252 : Cannot VRFY (verify) the user – the server will accept the message and attempt to deliver it
The user account appears to be valid but could not be verified, however the server will try do deliver the message.
SMTP Error 354 : Start mail input end with <CRLF>.<CRLF>
This is normally in response to the DATA command. The server has received the From and To information and is now asking for the "Message Body", the main part of the message which should be ended by two blank lines separated by a dot (period).
SMTP Error 421 : <Server name> Service not available – the sending email program should try again later
The Mail transfer service is unavailable because of a transient event. It generally indicates that the mail server which returns this status code is currently unavailable but may be available later.
SMTP Error 422 : The recipient’s mailbox is over its storage limit
Either the recipient’s mailbox is over its storage limit or the message delivery directory (folder) on the recipient’s mail server is currently over a size limit imposed by the Network Administrator.
SMTP Error 431 : The recipient’s mail server is experiencing a Disk Full condition
The recipient’s mail server is experiencing a Disk Full error condition, or an Out of Memory error condition.
SMTP Error 432 : The recipient’s Exchange Server incoming mail queue has been stopped
This is an SMTP status response specific to Microsoft Exchange Server. It indicates that the recipient’s mail queue on their Exchange Server has been stopped.
SMTP Error 441 : The recipient’s server is not responding
This is an error emanating from your server indicating that the recipient’s server is not responding. Your server will automatically try again a number of times – how many depends on how your server has been configured.
SMTP Error 442 : The connection was dropped during transmission.
Your server started delivering the message but the connection was broken during transmission. This may be an unusual transient error – however, if it keeps happening you should investigate possible problems which could result in a network connection being broken.
SMTP Error 446 : The maximum hop count was exceeded for the message
The maximum hop count was exceeded for your message. The most likely cause of this error status code is that your message is looping internally on your server, internally between two of your organisation’s servers, or, sometimes, looping between your server and the recipient’s server.
SMTP Error 447 : Your outgoing message timed out.
Your outgoing message timed out because of problems with the receiving server who objected to your message. Typically there is a problem with the message header, such as too many recipients, in most cases, or a protocol timeout between the two servers.
SMTP Error 449 : Routing error
This is a Microsoft Exchange Server specific error code. Possible causes may be : an SMTP connector is configured to use DNS without a smart host and also uses a non-SMTP address space (e.g. X.300), or A message was sent to a recipient who was identified as a member of a routing group that was deleted.
SMTP Error 450 : Requested action not taken – The mailbox was unavailable at the remote end.
In general SMTP Error 450 is a transient error at the remote end, and should induce your mail server to retry after it’s preset retry interval.
e.g. "450 Please try again later" -or- "SMTP Error 450 5.2.3 Msg Size greater than allowed by Remote Host"
SMTP Error 451 : Requested action aborted – Local error in processing.
The action has been aborted by the ISP’s server. "Local" refers to the ISP’s server. This error is usually due to overloading at the ISP from too many messages or transient failures.
e.g. "SMTP error 451 Unable to complete command, DNS not available or timed out" -or- "451 Domain of sender address does not resolve"
SMTP Error 452 : Requested action not taken – Insufficient storage.
The ISP server’s disk system has run out of storage space, so the action had to be cancelled.Sometimes this error may raise if your ISP’s mail server is overloaded from too many messages.
e.g. "452 Out of memory"
SMTP Error 465 : Code Page unavailable on the recipient server
This is an Exchange Server-specific error code. This error is returned by the recipient’s server if the incoming email specifies a Code Page that is not installed on the recipient’s server.
SMTP Error 471 : This is a local error with the sending server and is often followed with "Please try again later"
This is always a local error with your own mail server.It is usually caused by anti-spam or virus scanning software on your server (the sending server) getting into problems through a bug in the software, or because of a bad automatic update from the antivirus/anti-spam manufacturer, because of lack of memory on your server, or because of hard disk problems.
SMTP Error 500 : Syntax error command not recognized.
The last command sent by your server was not recognized as a valid SMTP or ESMTP command, or is not formatted in the way the server expected. This includes situations where the command is too long.
SMTP Error 501 : Syntax error in parameters or arguments (e.g. invalid email address)
The command was correct and recognised, but the parameters (the arguments, e.g. email address) were not valid. For example you try to use invalid email address as sender\@domain.com and as "\" is not allowed in email addresses.
e.g. "Remote host said: 501 Invalid Address"
SMTP Error 502 : Command not implemented.
The command or function issued by your mail server is valid but has not been activated.
SMTP Error 503 : Bad sequence of commands.
In the original standards SMTP Status 503 indicates that the commands have been sent in the wrong order, for example your mail server has sent the "Hello" command before sending the "Mail" command. This can often be caused by a drop in network connection just as your server was sending a command, resulting in the ISP’s server not receiving it and consequently not understanding the command that followed it.
SMTP Error 504 : Command parameter not implemented.
The command and parameter are both valid, but the parameter is not implemented on the ISP server, or an additional parameter or action is missing. For example, an often encountered SMTP Error 504 is : "504 Need to authenticate first".
SMTP Error 510 : Bad Email Address
Bad email address. This status code is generated by the sender’s local mail server.
SMTP Error 511 : Bad Email Address
Bad email address. This error is similar to error 510 and as with error 510, this status code is generated by the sender’s local mail server.
SMTP Error 512 : The host server for the recipient’s domain name cannot be found (DNS error)
This SMTP reply code is received when one of the servers on the way to the destination is unable to resolve the domain name of a recipient email address.
e.g. "SMTP Error 550 5.1.2 Host unknown – host cannot be found"
SMTP Error 513 : Address type is incorrect (most mail servers)
This status code is received if the email addresses are not defined correctly from the sender’s mail server. The may happend due to if a user try to copy and paste the mail addresses from a web page without setting it to correct format. For example the address like receiver(at)domian.com is invalid and should be formated like email@example.com before using.
e.g. "SMTP error 501 5.1.3 Invalid address" -or- "SMTP error 553 5.1.3 User address required !" -or- "SMTP error 501 5.1.3 Bad recipient address syntax"
SMTP Status 523 : The Recipient’s mailbox cannot receive messages this big
This error will be received when the total size of the message you have sent (ie: message + all of its attachments) exceeds the size limits on the Recipient’s server.
e.g. "SMTP Error 450 5.2.3 Message Size greater than allowed by Remote Host" -or- "SMTP Error 552 5.2.3 Data size exceeds maximum permitted" -or- "SMTP Error 552 5.2.3 Message exceeds maximum fixed size"
SMTP Error 550 : Requested actions not taken as the mailbox is unavailable.
SMTP Error 550 will be returned by many servers If the recipient email address simply does not exist on the remote side.
e.g. "550 Invalid recipient" -or- "550 User account is unavailable" -or- "550 No such user here"
SMTP Error 551 : User not local or invalid address – Relay denied.
If neither the sending mail address nor the recipient’s address are locally hosted by the server, then the ISP’s servers may refuse to relay the message on.
SMTP Error 552 : Requested mail actions aborted – Exceeded storage allocation.
The recipient’s mailbox has reached its maximum allowed size.
e.g. "552 sorry, mailbox firstname.lastname@example.org is over quota temporarily (#5.1.1)"
SMTP Error 553 : Requested action not taken – Mailbox name invalid.
There is an invalid email address in the "To", "CC", or "BCC" field of the email message.
SMTP Error 554 : Transaction failed.
There was a permanent error trying to complete the mail transaction which will not be resolved by resending the message in its current form. Some change to the message and/or destination must be made for successful delivery.