cannot connect to SMTP server: [101] Network is unreachable

[wyang]

Zabbix email notification failed with the error message:
cannot connect to SMTP server: [101] Network is unreachable

Zabbix server version: 2.4.8

Telnet to the mail server port 25 works.

Any idea what's causing the issue? Any idea where I'd start to troubleshoot what's causing the issue? Thanks in advance.

[wyang]

The Zabbix server has two NICs configured.
- NIC 1 is configured with a private IP, which is the server IP that Zabbix agents are configured.
- NIC 2 is configured with a public IP, which is expected to the the IP to send email notification.

How to configure Zabbix server to fix the issue of alert notification? Thanks.

[wyang]

I look forward to any suggestions on how to fix the issue. Thanks!