We have K2 server, Sql Server & SharePoint and these are on-premises. Recently we moved all three server from on-premise to a private cloud. Everything works fine from K2 to Sql server & K2 to SharePoint, email is also working from SharePoint and email is working with K2 Server as well but it is only email used in Mail Event.

The email of Default Client Event is not working and following error is found in the error log:

61007 Permanent failure sending message adf: System.Net.Mail.SmtpException: Failure sending mail. ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host

There are many post related to above error and I tried all but couldn't resolved the issue. 

I tried to change k2 service account config in k2hostserver.exe.config and got the following error :

<system self="K2:denallixk2prd" enableListeners="true" allowAmbiguity="true" />

61007 Permanent failure sending message adf: System.ArgumentException: The parameter 'address' cannot be an empty string.
Parameter name: address

I also tried to change the smtp from ConnectionStringEditor, but couldn't resolve it.

Any help would be much appriciated.

Thanks,