Symptoms

_1
Smartforms Email rule errors with:
The remote name could not be resolved: 'K2SmartActions@denallix.com'

_2
7498 An error has occurred: System.Exception: Exception has been thrown by the target of an invocation. : The EventBusInterop Container property is null.
at SourceCode.EventBus.Server.EventQueueProcessing.ExecuteAssembly(Int32 CustomEventInstanceID, Int32 CustomEventID, ResolvedPolicyMapping resolvedPolicyMapping, Boolean isConditional, Int32 eventTypeID)
at SourceCode.EventBus.Server.EventQueueProcessing.ProcessEvent(Int32 ID)

7008 The following error occurred while executing policy for CustomEventInstanceID: 479 : Exception has been thrown by the target of an invocation. : The EventBusInterop Container property is null..

_3
SendOnly cannot be used by a user without a mailbox. Use SendAndSaveCopy and specify a folder ID in a mailbox to send an item from an account that doesn't have a mailbox.
 

Diagnoses

_1
The "Mail Server" environment library field had the incorrect SMTP server value.

_2
There was an EWS connection string that was null.

_3
Smartactions was enabled and the K2 Service account was specified in the "self" node this account does not have a mailbox.
 

Resolution

_1
Updating the "Mail Server" to a hostname that was accessible internally resolved this error.

_2
Removing this null entry using the ConnectionStringEditor.exe and restarting the K2 blackpearl service resolved this error.

_3
There was another "K2 Smartactions" account that had a mailbox, as such we configured the "self" node as well as values for the EWS connection strings to use this account instead. Restarting the K2 blackpearl service resolved this error.