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Email / SMTP Response and Error Numbers

Category: Getting Started

Simple Mail Transfer Protocol i.e., SMTP is used for sending and receiving emails. Whenever an email is rejected by the third party server or by the parent email server, then SMTP produces a specific Error/Response, which can be used to troubleshoot/identify the cause of email delivery failure. We gathered most of the SMTP errors/responses users most likely encounter when performing email practises. Going further, we also included the Error/Response description and possibly responsible for the SMTP error/response and that too covered individually. You can click on the Error/Response Code or the Resolution link to learn more about the error and solution (if available) individually.

SMTP Response NumberDefinitionHow to Resolve / Examples
101Cannot open connectionHow to fix SMTP Error 101
Examples:“SMTP Error 101, Error opening connection”
Examples:“SMTP Error 101, cannot open SMTP stream”
111Connection refused or inability to open an SMTP streamHow to fix SMTP Error 111
211System status message or system help replyHow to fix SMTP Error 211
214Help message (Information on non-standard command)How to fix SMTP Error 214
220<SERVER> Service readyHow to fix SMTP Error 220
221<SERVER> Service closing transmission channelHow to fix SMTP Error 221
Examples:“221 Closing connection”
Examples:“221 Goodbye”
250Requested mail action okay, completedHow to fix SMTP Error 250
251User not local; will forward to <REMOTEPATH>How to fix SMTP Error 251
252Can not verify user; accepting message for attemptHow to fix SMTP Error 252
354Starting mail inputHow to fix SMTP Error 354
420Timeout connection problemHow to fix SMTP Error 420
NOTE:This error is related to GroupWise Servers only.
421<SERVER> Service not available, closing transmission channelHow to fix SMTP Error 421
431Not enough storage or out of memory (See #452, #552)How to fix SMTP Error 431
432Recipients Exchange Server incoming mail queue stoppedHow to fix SMTP Error 432
NOTE:This error is related to Microsoft Exchange Servers only.
441Recipients mail server is not respondingHow to fix SMTP Error 441
442Connection dropped during transmissionHow to fix SMTP Error 442
446The maximum hop count was exceeded for the message: an internal loop has occurred.How to fix SMTP Error 446
447Your outgoing message timed out because of issues concerning the incoming server.How to fix SMTP Error 447
449A routing error.How to fix SMTP Error 449
NOTE:This error is related to Microsoft Exchange Servers only.
450Requested mail action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)How to fix SMTP Error 450
Examples:“450 Please try again later”
“SMTP Error 450 5.2.3 Msg Size greater than allowed by Remote Host”
451Requested action aborted: error in processingHow to fix SMTP Error 451
Examples:“SMTP error 451 Unable to complete command, DNS not available or timed out”
“451 Domain of sender address does not resolve”
452Requested action not taken: insufficient system storageHow to fix SMTP Error 452
Example:“452 Out of memory”
455Server unable to accommodate parametersHow to fix SMTP Error 455
471An error of your mail server, often due to an issue of the local anti-spam filterHow to fix SMTP Error 471
500Syntax error, command unrecognized (This may include errors such as command line too long)How to fix SMTP Error 500
501Syntax error in parameters or arguments
How to fix SMTP Error 501
Example:“Remote host said: 501 Invalid Address”
502Command not implementedHow to fix SMTP Error 502
503Bad sequence of commandsHow to fix SMTP Error 503
504Command parameter not implementedHow to fix SMTP Error 504
510Invalid email addressHow to fix SMTP Error 510
511Invalid email address (See #552)How to fix SMTP Error 511
512A DNS error: the host server for the recipient’s domain name cannot be found.How to fix SMTP Error 512
Example:“SMTP Error 550 5.1.2 Host unknown – host cannot be found”
513Address type is incorrect (possibly misspelled)How to fix SMTP Error 513
“SMTP error 501 5.1.3 Invalid address”
Examples:“SMTP error 553 5.1.3 User address required !”
Examples:“SMTP error 501 5.1.3 Bad recipient address syntax”
521<DOMAIN> does not accept mailHow to fix SMTP Error 521
Example:“521 5.2.1 : (CON:B1)
523The total size of your mailing exceeds the recipient server’s limitsHow to fix SMTP Error 523
Examples:“SMTP Error 450 5.2.3 Message Size greater than allowed by Remote Host”
Examples:“SMTP Error 552 5.2.3 Data size exceeds maximum permitted”
Examples:“SMTP Error 552 5.2.3 Message exceeds maximum fixed size”
530Normally, an authentication problem. But sometimes it’s about the recipient’s server blacklisting yours, or an invalid email address.How to fix SMTP Error 530
541The recipient address rejected your message: normally, it’s an error caused by an anti-spam filter.How to fix SMTP Error 541
550Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)How to fix SMTP Error 550
Examples:“550 Invalid recipient”
Examples:“550 User account is unavailable”
Examples:“550 No such user here”
551User not local; please try <FORWARDPATH>How to fix SMTP Error 551
552Requested mail action aborted: exceeded storage allocationHow to fix SMTP Error 552
Example:“552 sorry, mailbox is over quota temporarily (#5.1.1)”
553Requested action not taken: mailbox name not allowed (e.g., mailbox syntax incorrect)How to fix SMTP Error 553
554Transaction failed (Or, in the case of a connection-opening response, “No SMTP service here”)How to fix SMTP Error 554
555MAIL FROM/RCPT TO parameters not recognized or not implementedHow to fix SMTP Error 555

(Ref: SMTP Protocol RFC )

Provider Specific Error Responses

Gmail SMTP Error Responses