Qlik Alerting- Email Server: Unexpected socket close

[LanBiteam]

Hello,

I am configuring the Qlik Alerting # for the first time. When I enter our E-Mail server. There is error shows "Email server: Unexpected socket close.

Is this a problem from the configuration data? The ports of the server is open.

Since the same smtp server is also used by the other products. The email server should be fine. 

Thanks in advance.

Best,

Lan