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VMware SMTP configuration - Deep dive


Notification mails are not just a part of an IT administrator’s life, it is the lightening before a thunder. If they miss these notification emails, anything could burst out in the environment! So settings SMTP for the vCenter is highly recommended, most importantly it should work :) 

For the past two weeks I had a chance to learn a lot about sendmail functionality in VCSA, so I’d like to share this with you. 


What is sendmail ?
Sendmail is a unix/linux OS based SMTP. It is a mail transfer agent (MTA) which is used to deliver or route email. VMware uses sendmail to notify the alarms as notification emails.

How to setup SMTP?
SMTP is a straight forward configuration, go to "configure" on the vCenter configuration tab, under “settings” look for "mail" and then provide the mail server name along with the mail address where it has to be sent.

What happens if it does not work?
Now once the SMTP configured, you perform a test alarm and if the mail is triggered, its well and good. you and the customer can go home happily. Will this happen all the time? mm not really.  We need to check two layers to see if the SMTP is working correctly.

1. To see if the mail is queued on the vCenter, running the #mailq command on the vCenter Server Appliance displays pending emails.

2. To see if sendmail is actually working or not. Please find the approach which i tried to find the root cause.

a. check the log file -> /var/log/messages, here look for the key work - "mailer" we can find the error messages.
   also check the log file /var/log/vmware/vmware-vpx/vpxd.log -> keyword "SMTP" these two log files are more than enough to understand the issue.

b. you can run the below echo command to test if sendemail feature actually works.
 # echo “Subject: sendmail test” | sendmail -v test.com    ( if this fails, you get an output of the mail transaction right away.)

c. It is worth checking the DNS and resolve the mail server from the vCenter, this was the issue in my case. we are unable to resolve the mailserver although the mailserver is able to telnet and ping from the vCenter, so it was an issue on the customers mail server end.

d. If all the above steps failed, then move on to modify the sendmail.cf and sendmail.mc - configuration files. you can follow the KB - https://kb.vmware.com/s/article/54375

Please be aware that the configuration file of Sendmail is sendmail.cf. This file is a product of the macro configuration file, sendmail.mc and you have to make configuration changes on the macro file and restart the services and daemon.

#systemctl daemon-reload
#systemctl restart sendmail  

Known issues -> Email alerts not working after upgrading to vCenter 6.5 U1 -> https://kb.vmware.com/s/article/49725  
                         -> Emails sent from VMware vCenter Server Appliance are rejected ->  https://kb.vmware.com/s/article/2073849

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