The mail service uses the syslogd program to log error messages. These messages are logged for reference when resolving issues.
Your mail service logs most error messages by using the syslogd program. By default, the syslogd program sends these messages to a system called loghost, which is specified in the /etc/hosts file. You can define loghost to hold all logs for an entire NIS domain. If no loghost is specified, error messages from syslogd are not reported.
The /etc/syslog.conf file controls where the syslogd program forwards messages. You can change the default configuration by editing the /etc/syslog.conf file. You must restart the syslog program for any changes to become active.
To gather information about mail, you can add the following selections to the file:
mail.alert – Messages about conditions that should be fixed immediately
mail.crit – Critical messages
mail.warning – Warning messages
mail.notice – Messages that are not errors but might need attention
mail.info – Informational messages
mail.debug – Debugging messages
For more information, see the syslog.conf(4) man page.
The following entry in the /etc/syslog.conf file sends a copy of all critical, informational, and debug messages to /var/log/syslog.
mail.crit;mail.info;mail.debug /var/log/syslog
Each line in the system log contains a timestamp, the name of the system that generated the line, and a message. The syslog file can log a large amount of information.
The log is arranged in a succession of levels. The lowest level logs only unusual occurrences. The highest level logs every event that takes place. As a convention, log levels under 10 are considered to be useful. Log levels that are higher than 10 are usually used for debugging. The default level (9) has the right balance for most sites. For more information, see Customizing System Message Logging in Troubleshooting System Administration Issues in Oracle Solaris 11.3.
This section describes how you can resolve some common sendmail-related error messages. For more information, see Open Source Frequently Asked Questions (https://web.archive.org/web/20161027034616/http://www.sendmail.com:80/sm/open_source/support/support_faq).
Error: 451 timeout waiting for input during source
Cause: When sendmail reads from a source that might time out, such as an SMTP connection, the program sets a timer to a value of various –Timeout options before reading begins. If the read is not completed before the timer expires, this message appears and reading stops. Usually, this situation occurs during RCPT. The mail message is then queued for later delivery. For more information, see the sendmail(1M) man page.
Solution: If you see this message often, increase the value of various –Timeout options in the /etc/mail/sendmail.cf file. If the timer is already set to a large number, check for hardware problems such as poor network cabling or connections.
Error: 550 hostname... Host unknown
Cause: The destination host system, which is specified by the portion of the address after the @ sign (at), was not found during domain name system (DNS) lookup.
Solution: Use the nslookup command to verify that the destination host exists in that domain or other domains. Also check whether you have typed the wrong domain. If the domain does not exist, contact the intended recipient and ask for a proper address.
Error: 550 username... User unknown
Cause: The intended recipient, who is specified by the portion of the address before the @ sign (at), could not be located on the destination host system.
Solution: Check whether you have typed the wrong email address and try again. If this remedy does not work, contact the intended recipient and ask for a proper address.
Error: 554 hostname... Local configuration error
Cause: The local host is trying to send mail to itself.
Solution: Check the value of the $j macro in the /etc/mail/sendmail.cf file to ensure that the value is a fully qualified domain name.
Description: When the sending system provides its host name to the receiving system in the SMTP HELO command, the receiving system compares its name to the sending system's name. If these names are the same, the receiving system issues the error message and closes the connection. The name that is provided in the HELO command is the value of the $j macro.
Error: config error: mail loops back to myself.
Cause: This error message occurs when you set up an MX record. Host host1 is made the mail exchanger for domain domain1 but the host is not configured. Another possibility is that both the sending system and the receiving system are identified as the same domain.
Solution: Search in Open Source Frequently Asked Questions (https://web.archive.org/web/20161027034616/http://www.sendmail.com:80/sm/open_source/support/support_faq).
Error: user unknown
Cause: The intended recipient on the same system cannot be located.
Solution: Some possible solutions:
Check for a typographical error in the entered email address. The user might be aliased to a nonexistent email address in /etc/mail/aliases or in the user's .mailrc file.
The user name might use uppercase characters. Preferably, email addresses should not be case sensitive.