vCenter stopped sending emails without any change in the network or vCenter

Products

• VMware vCenter Server

Issue/Introduction

This article provides an alternative step to restore vCenter emails alert setting, without following KB 54375 or rebooting the vCenter. Further, it clarifies minimum requirements on DNS settings for vCenter email alerts.

Symptoms:

vCenter could send outgoing emails to the mail server before it stopped sending emails, and there is no change in either the network (IP, DNS, mail server) or vCenter.

 

In the messages.log, below log could be observed.

2023-07-04T16:02:39.176093+08:00 gzvctsvr5 sendmail[45801]: 36482duh045799: to=<email_id1@example_test.com>,<email_id2@example_test.com>, delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=151225, relay=example_test.com, dsn=5.1.2, stat=Host unknown (Name server: example_test.com: no data known)

 

 

Environment

VMware vCenter Server 7.0.x, 8.0.x

Cause

vCenter is not working properly however the reason is not clear.

Resolution

Use below command to ensure the mail server is working, please change the mail server IP accordingly:

nc -v 192.168.1.10 25

 

In vCenter GUI, Menu -> Inventory -> Configure -> General (under Settings) -> Edit, Change the Mail server under Mail section, firstly change it to a wrong IP and save, then change it back to the original correct IP and save.

 

Additional Information

When we look at the log, it seems the DNS for example_test.com is not properly configured. Actually example_test.com is the domain name for the sender and receiver, there is no A or MX type DNS record for it. And customer uses an IP address as the mail server, which is not related to example_test.com. So it is suspicious there is "relay=example_test.com" in the log, if we follow the resolution in this KB, it will work properly which means the email is forwarded to the mail server from vCenter. And it confirms that there is no need to have DNS setting for the sender/receiver's domain, assuming the mail server does not have any restriction settings.

Impact/Risks:

vCenter could not send email alert when the alert is triggered.