Host Unknown (Hard bounce)

This error is returned when the domain part (the string to the right of the "@" symbol) of the destination email address is an unknown host or a non-existent domain name. In many cases, this is caused by a typo in the domain name, an invalid DNS record, or a domain that has been discontinued. In Sisimai's internal processing, this reason is also determined when the value of the Status: field in the bounce email is "5.1.2".

Your message to the following recipients cannot be delivered:

<kijitora@example.cat>:
<<< No such domain.
                

User Unknown (Hard bounce)

This error is returned when the local part (the string to the left of the "@" symbol) of the destination email address is a non-existent user. This is often the case for users who have changed their email address (for mobile phones) or have canceled their provider subscription (for PCs), or for users who have left a company or organization.

<kijitora@example.co.jp>: host mx01.example.co.jp[192.0.2.8] said:
  550 5.1.1 Address rejected kijitora@example.co.jp (in reply to RCPT TO command)
                

In Sisimai's internal bounce email processing, this reason is determined when the value of the "Status:" field is "5.1.1", when the connection is rejected with RCPT TO: in the SMTP session, or when the "Diagnostic-Code:" header indicates that the recipient is unknown.

Filtered

This error is returned when the user has configured their email settings to reject emails, or when the mailbox exists but is not receiving emails. For deliveries to mobile phones in Japan (3 major carriers), this reason is determined if the domain is blocked (excluded from domain-specified reception) or if the email is rejected by a URL filter.

This error reason is nearly identical to UserUnknown.

... while talking to mfsmax.ntt.example.ne.jp.:
>>> DATA
<<< 550 Unknown user kijitora@ntt.example.ne.jp
554 5.0.0 Service unavailable
                

In Sisimai's internal bounce email processing, this reason is also determined when the value of the "Status:" field is "5.2.0" or "5.2.1", or when the email is rejected based on the content after the DATA command in the SMTP session.

Has Moved (Hard bounce)

This error is returned when the recipient's mailbox has been moved to another address (and automatic forwarding is not set up). In Sisimai's internal bounce email processing, this reason is determined when the value of the "Status:" field is "5.1.6".

<kijitora@example.go.jp>: host mx1.example.go.jp[192.0.2.127] said: 550 5.1.6 recipient
no longer on server: kijitora@example.go.jp (in reply to RCPT TO command)
                

Rejected

This error is returned when the email is rejected by the sender's address (Envelope From). In Sisimai's internal bounce email processing, this reason is determined when the value of the "Status:" field is "5.1.8", or when the email is rejected based on the content of the MAIL FROM: command in the SMTP session.

<kijitora@example.org>:
Connected to 192.0.2.225 but sender was rejected.
Remote host said: 550 5.7.1 <root@nijo.example.jp>... Access denied
                

Mailbox Full

This error is returned when the recipient's mailbox is full (exceeding the maximum storage capacity specified by the mail server). This applies to both mobile phones and PCs, and occurs when the user has not received emails and left them on the server, or has received emails but has not deleted them from the server.

Action: failed
Status: 5.2.2
Diagnostic-Code: smtp;550 5.2.2 <kijitora@example.jp>... Mailbox Full

In Sisimai's internal bounce email processing, this reason is determined when the value of the "Status:" field is "4.2.2" or "5.2.2". This error is returned when the email is rejected by the sender's address (Envelope From).

Suspend

This error is detected when the user has unpaid charges for au by KDDI. This error may also occur if the account is temporarily suspended for some reason, even for emails to Gmail or Yahoo!.

SMTP error from remote mail server after end of data: host mx2.mail.yahoo.com [192.0.2.222]:
554 delivery error: dd Sorry your message to **@yahoo.com.ar cannot be delivered.
This account has been disabled or discontinued [#102]. - mta497.mail.mud.yahoo.com"
                

Auth Failure

This error is returned when domain authentication using SPF, DKIM, DMARC, or ARC fails. It often occurs when domain authentication fails in multiple factors, such as when it fails in both SPF and DKIM. This bounce reason was implemented in Sisimai 5.0.0.

Action: failed
Status: 5.7.26
Remote-MTA: dns; gmail-smtp-in.l.google.com
Diagnostic-Code: smtp;
    550-5.7.26 This mail has been blocked because the sender is unauthenticated.
    550-5.7.26 Gmail requires all senders to authenticate with either SPF or DKIM.
    550-5.7.26 Authentication results:
    550-5.7.26  DKIM = did not pass
    550-5.7.26  SPF [relay3.example.com] with ip: [192.0.2.22] = did not pass
    550-5.7.26 For instructions on setting up authentication, go to
    550 5.7.26 https://support.google.com/mail/answer/81126#authentication
    c2-202200202020202020222222cat.127 - gsmtp
                

Bad Reputation

This error is returned when the sender's IP address or domain has a low reputation score on the receiving host, and the email is rejected for that reason. You may see this error when sending to large email service providers such as Gmail or Outlook. This bounce reason was implemented in Sisimai 5.0.0.

Action: failed
Status: 5.7.1
Remote-MTA: dns; gmail-smtp-in.l.google.com
Diagnostic-Code: smtp; 550-5.7.1 [192.0.2.22      18] Our system has
    detected that this message is 550-5.7.1 likely suspicious due to the very
    low reputation of the sending IP 550-5.7.1 address. To best protect our
    users from spam, the message has been 550-5.7.1 blocked. Please visit 550
    5.7.1  https://support.google.com/mail/answer/188131 for more information.
    p22nn000202cat.22 - gsmtp
                

Blocked

This bounce reason is determined by Sisimai when the connection to the destination host is rejected due to the IP address, hostname, or EHLO, EHLO command value of the sending mail server. This bounce reason was implemented in Sisimai 4.0.0 and is not implemented in bounceHammer.

<kijitora@example.net>: 
Connected to 192.0.2.112 but my name was rejected. 
Remote host said: 501 5.0.0 Invalid domain name
                

Expired

This error category includes emails that are bounced back due to delivery timeouts, such as when the email cannot connect to the destination host. If the reason for the delivery failure is DNS resolution, the bounce reason may be NetworkError.

kijitora@example.org
(ultimately generated from nekochan@example.org)
all hosts have been failing for a long time and were last
tried after this message arrived
                

Mailer Error

This error is returned when the program that is supposed to be launched upon receiving an email fails to terminate normally. This is often caused by a bug in the program or insufficient exception handling when connecting to a required backend service (such as a database).

X-Actual-Recipient: X-Unix; |/home/kijitora/mail/catch.php
Diagnostic-Code: X-Unix; 255
                

Network Error

This bounce reason is determined by Sisimai when an SMTP connection cannot be established due to DNS resolution failure or other network-related errors that prevent the email from being sent. This bounce reason was implemented in Sisimai 4.1.12 and is not implemented in bounceHammer.

A message is delayed for more than 10 minutes for the following
list of recipients:

kijitora@neko.example.jp: Network error on destination MXs

No Relaying

This bounce reason is determined by Sisimai when an email is bounced due to SMTP relay rejection. This bounce reason is not implemented in bounceHammer.

... while talking to mailin-01.mx.example.com.:
>>> RCPT To:<kijitora@example.org>
<<< 554 5.7.1 <kijitora@example.org>: Relay access denied
554 5.0.0 Service unavailable
                

Not Accept

This error is returned when the recipient's mail server cannot receive the email. This error can occur if the destination mail server is overloaded or under maintenance. In the internal process of the bounce email processing performed by Sisimai, this reason is determined for emails with a "5.3.2" value in the "Status:" field or a "556" value in the SMTP reply code. Additionally, this bounce reason also includes cases where the sender domain is a NullMX.

Require PTR

This error is returned when the PTR record (reverse lookup record) is not set or is incorrect for the source IP address that made the SMTP connection. Some email service providers strictly verify reverse lookups, so at least some reverse lookup configuration is required.

Action: failed
Status: 5.7.25
Remote-MTA: dns; gmail-smtp-in.l.google.com
Diagnostic-Code: smtp; 550-5.7.25 [192.0.2.202] The IP address sending this
    message does not have a 550-5.7.25 PTR record setup, or the corresponding
    forward DNS entry does not 550-5.7.25 point to the sending IP. As a policy,
    Gmail does not accept messages 550-5.7.25 from IPs with missing PTR
    records. For more information, go to 550 5.7.25
    https://support.google.com/mail/answer/81126#ip-practices
    neko-1785a7g6767a6agg.2 - gsmtp
                

This bounce reason was implemented in Sisimai 5.0.0 as a separate category from Blocked.

Speeding

This error occurs when the recipient host has a per-unit-time traffic limit and that limit has been exceeded. This means that the sender's email sending speed is too fast. This bounce reason was implemented in Sisimai 5.0.0 as a separate category from Security Error or Too Many Conn.

Status: 5.2.1
Remote-MTA: dns; alt1.gmail-smtp-in.l.google.com
Diagnostic-Code: smtp; 550-5.2.1 The user you are trying to contact is
    receiving mail at a rate that 550-5.2.1 prevents additional messages from
    being delivered. For more 550-5.2.1 information, please visit 550 5.2.1
    https://support.google.com/mail/?p=ReceivingRatePerm p131si8414989oif.118 -
    gsmtp
                

System Error

This bounce reason is classified when a bounce occurs due to a system error on the recipient's mail server, such as a connection failure to the LDAP server.

<kijitora@example.net>: 
Unable to contact LDAP server. (#4.4.3)I'm not going to try again; this
message has been in the queue too long.
                

System Full

This error is returned when the recipient's mail server's disk is full. This indicates that the recipient host cannot receive any more emails. In the internal process of bounce email processing performed by Sisimai, this reason is determined for emails with a "5.3.1" or "4.3.1" value in the "Status:" field.

Too Many Connections (toomanyconn)

When a large number of connections are made to the recipient's SMTP server at the same time, new SMTP connections may be temporarily rejected. In such cases, the bounce email returned will be classified into this bounce reason by Sisimai.

<kijitora@example.ne.jp>: host mx02.example.ne.jp[192.0.1.20] said:
452 4.3.2 Connection rate limit exceeded. (in reply to MAIL FROM command)