Plesk BU - Event log error, The message could not be sent to the SMTP server

[LeaUK]

System.Web.HttpException: Could not access 'CDO.Message' object. ---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Runtime.InteropServices.COMException (0x80040211): The message could not be sent to the SMTP server. The transport error code was 0x800ccc15. The server response was not available

Seems like Plesk BU cannot talk to my local SmarterMail 4.x mail server - any tips?


Cheers
Lea