SMTP Error Messages

SMTP Response Codes and Errors

Simple Mail Transfer Protocol (SMTP) is an internet standard for email transmission.
SMTP is a text based protocol in which the sender communicates with the mail receiver by issuing commands and receiving a response code.

 

Sample:

C: MAIL FROM:<someone@arclab.com>
S: 250 Ok

In this sample the client issues the MAIL FROM command and the server replies with 250 Ok.

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The following (incomplete) list of response codes and error messages should help finding errors in your mail settings.
It contains common problems and error messages.

 

SMTP Error 221

221 <domain> Service closing transmission channel
221 Closing transmission
221 Goodbye

Error 221 is an authentication error, which means you are using the wrong mail server, the user/password is incorrect, you need to change the authentication method or SMTP access is not enabled for your email account. Try using SSL/TLS if you are sure that the mail server and user/password is correct.

Note: SMTP access in disabled by default on some accounts, e.g. when using Gmail you need to enable "less secure apps" (third party apps) in the Gmail settings: https://support.google.com/accounts/answer/6010255?hl=en

 

 

 

SMTP Error 421

421 Temporary System Problem. Try again later.
421 Try again later, closing connection.
421 Server busy, try again later.

The SMTP error 421 is normally used for temporary problems on the mail server or a problem with the recipients email account.
Some mail providers might also return 421 after you reached a limit (restriction) on your mail account (see SMTP Error 451 below).

 

 

SMTP Error 451

451 4.3.0 Mail server temporarily rejected message
451 You have exceeded your messaging limits

If you receive one of the above (or a similar) error message from your mail server (after you've sent out some messages), then you have reached a limit on your mail server (or email account). This means your mail server will not accept any further messages until you waited some time.

Your mail account might have one or multiple limitations:

Note: No mail software can send more messages as your mail server (or email account) allows. It's a limitation of the used email account and not a program limit or software bug. Please contact your mail administrator or mail provider for further details on your account limits for SMTP mail (outgoing messages).

If the used email account is too restrictive, use a different email account (and mail server) instead. It's recommended to use an email account from your own domain (website), your company mail server or a business email account. In general a business account should have less mailing restrictions than a free account.

MailList Controller can be adjusted to such a limit, see our FAQ for details.

 

 

SMTP Error 530

530 Authentication Required
530 5.7.0 Must issue a STARTTLS command first

Check the authentication (username/password) and enable SSL/TLS (StartTLS) in the account settings of your mail client, if required.
If you are using MailList Controller, change the authentication method to "StartTLS" (Details).

 

 

SMTP Error 550

550 Requested action not taken: mailbox unavailable [E.g., mailbox not found, no access]
550 5.7.1 unable to relay for
550 The email account that you tried to reach is disabled
550 Invalid recipient
550 No such user here

You will get this error when you try to send an email to an invalid email address or if you need to authenticate before sending an email.
Some providers also use error 550 to indicate that you reached your send (relay) limit:

550 5.4.5 Daily sending quota exceeded
550 5.7.1 Email quota exceeded
550 5.7.1 Daily SMTP relay limit exceeded for customer

See: "SMTP Error 553" (below) for details.

 

 

 

SMTP Error 553

553 Requested action not taken: mailbox name not allowed
553 Mailbox name invalid

Check the recipient's email address: either the email address does not exist or there is a syntax error. Also check additional recipients in CC and BCC.

553 Sorry, over your daily relay limit
553 Too many mail
553 Quota exceeded

If you receive one of the above (or a similar) error message from your mail server (after you've sent out some messages), then you have reached a limit on your mail server (or email account). This means your mail server will not accept any further messages until you waited some time.

Your mail account might have one or multiple limitations:

Note: No mail software can send more messages as your mail server (or email account) allows. It's a limitation of the used email account and not a program limit or software bug. Please contact your mail administrator or mail provider for further details on your account limits for SMTP mail (outgoing messages).

If the used email account is too restrictive, use a different email account (and mail server) instead. It's recommended to use an email account from your own domain (website), your company mail server or a business email account. In general a business account should have less mailing restrictions than a free account.

MailList Controller can be adjusted to such a limit, see our FAQ for details.

Disclaimer: The information on this page is provided "as is" without warranty of any kind. Further, Arclab Software does not warrant, guarantee, or make any representations regarding the use, or the results of use, in terms of correctness, accuracy, reliability, currentness, or otherwise. See: License Agreement