How to connect Pop3/SMTP server on premise with D365 online

Hi everyone,

No, I'm going to setup Mdaemon 13  email server with D365 customer engagement online by Pop3/SMTP connect. I done all step as the below link. 

https://community.dynamics.com/365/b/dynamics365enterprisecloudfronts/archive/2018/04/25/how-to-setup-pop3-smtp-email-configuration-in-dynamics-crm

But I got the error message as the below

ActivityId: 01f2f8eb-be04-423b-bf57-ad4704be1479
>Error : System.Net.Mail.SmtpException: Failure sending mail. ---> System.Security.Authentication.AuthenticationException: The remote certificate is invalid according to the validation procedure.
at System.Net.Mail.SmtpConnection.ConnectAndHandshakeAsyncResult.End(IAsyncResult result)
at System.Net.Mail.SmtpTransport.EndGetConnection(IAsyncResult result)
at System.Net.Mail.SmtpClient.ConnectCallback(IAsyncResult result)
--- End of inner exception stack trace ---

Anybody know that issue? what do I do to send out email?

Thank for your support