Symptoms:

• vCenter Server Appliance 6.5 stops sending alert emails.
• You see a similar output when checking the status of sendmail:

root@vcsa [ /etc/mail ]# systemctl status sendmail
? sendmail.service - Sendmail Mail Transport Agent
Loaded: loaded (/etc/systemd/system/sendmail.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Thu 2017-12-28 14:46:52 EET; 7min ago
Process: 40811 ExecStart=/usr/sbin/sendmail -bd -q $QUEUE $SENDMAIL_OPTARG (code=exited, status=0/SUCCESS)
Main PID: 40813 (code=exited, status=71)

Dec 28 14:46:42 vcsa sendmail[40813]: NOQUEUE: --- 451 4.0.0 opendaemonsocket: daemon Daemon1: cannot bind: Address already in use (hold)
Dec 28 14:46:42 vcsa sendmail[40813]: NOQUEUE: SYSERR(root): opendaemonsocket: daemon Daemon1: cannot bind: Address already in use
Dec 28 14:46:42 vcsa sendmail[40813]: daemon Daemon1: problem creating SMTP socket
Dec 28 14:46:47 vcsa sendmail[40813]: NOQUEUE: --- 451 4.0.0 opendaemonsocket: daemon Daemon1: cannot bind: Address already in use (hold)
Dec 28 14:46:47 vcsa sendmail[40813]: NOQUEUE: SYSERR(root): opendaemonsocket: daemon Daemon1: cannot bind: Address already in use
Dec 28 14:46:47 vcsa sendmail[40813]: daemon Daemon1: problem creating SMTP socket
Dec 28 14:46:52 vcsa systemd[1]: sendmail.service: Main process exited, code=exited, status=71/n/a
Dec 28 14:46:52 vcsa systemd[1]: Stopped Sendmail Mail Transport Agent.
Dec 28 14:46:52 vcsa systemd[1]: sendmail.service: Unit entered failed state.
Dec 28 14:46:52 vcsa systemd[1]: sendmail.service: Failed with result 'exit-code'.

Note: The preceding log excerpts are only examples. Date, time, and environmental variables may vary depending on your environment.

VMware vCenter Server Appliance 6.5.x

Currently there is no resolution. VMware is actively investigating the issue to determine the root cause. If you encounter this issue please file a support request. 

Workaround:
To workaround the issue please perform the following steps. Ensure you have a snapshot or backup of the vCenter Server Appliance before proceeding. 

1. Download & extract the "sendmail_daemon_cron.sh.zip" and "sendmail_daemon_cron.cron.zip" file attached to this KB.
2. Using WinSCP or similar upload "sendmail_daemon_check.sh" to "/usr/sbin/" 
3. Complete the same process for the file "sendmail_daemon_check.cron" to "/etc/cron.d"  

Note: Permission should never contain "execution", change the permission to 666 for both files. 

Note: By default, the execution of cron to verify the daemon status is set to 30 mins. This can be modified by changing the value 30 to 'x' in minutes in 'sendmail_daemon_check.cron'. A restart of any service is not required. Crond will understand the changes automatically.

Impact/Risks:
Alert emails are not being sent.