Troubleshooting of sendmail issues in Linux machine

 

Troubleshooting of Sendmail issues:

Sendmail servers can produce some wide range of problems that any Unix server can generate, most daily Sendmail issues fall into just a few categories which is related to mail connection, Sendmail relay configuration and SMTP auth issues.

1) Email not deliverable:

We can able to valid whether user email ID or local domain is able to deliver from the system.

#sendmail -bv usernameEmailID
#sendmail -bv root@localdomain

2) Check the status of sendmail service. the mail server may go down if the server has a high workload.

#systemctl status sendmail

Start the sendmail if the service is down,

#systemctl start sendmail

3) Check the sendmail relay server details in the sendmail.cf configuration file.

#grep ^DS /etc/mail/sendmail.cf

The relay server should be resolve from the host, otherwise the mail request will not able to resolve by DNS and through Transient parse error -- message queued for future delivery error.

4) mqueue is got filled due to mail thread is not able to deliver or in the mail queue.

We used to face a var file system reached 100% utilization due to this problem.

    i) check the current status of mail

        #mailq

    ii) Try to deliver the pending mail queue 

        #sendmail -v -q

    iii) Stop the sendmail service

        #systemctl stop sendmail

    iv) move or delete the mqueue list

        #mv /var/spool/mqueue/* /temporary_location

      v) Start the sendmail service

        #systemctl start sendmail

5) Validated the sendmail functions

       i) send a testmail from the system

            # echo "This is test email" | mailx -v -s "Test mail subject" -S smtp="smtpserver:port" "usermail_ID"

      ii) Open a other terminal and monitor the mail thread 

            #tail -f /var/log/maillog

    

Sendmail Log location : /var/log/maillog

    iii) Check sendmail connectivity from the system

            #nc -vz sendmailsever 25

    iv) check the connection of sendmail

            #ps auxw| grep [a]ccepting

    v) check the system is listening of sendmail

            #netstat  -antp| grep sendmail