Symptoms

The Workflow doesn't send emails to the recipients (group, users, roles) using Notifications. Although it sends email using the Email Event.
 

Diagnoses

This was a result of two issues.
1: There were errors in the HostServer log indicating an issue with MSMQ.
Error: EventBus","7028","Initializing","MSMQ.TestConnectivity","7028 ' SERVERNAME]EventBus' queue does not exist, the queue will be created.

2. After resolving the issue with MSMQ, email did not send as there were no connection strings for the From address being used.
 

Resolution

1. It appears at one time the environment had been configured to use private queues, but at some point switched back to public queues. We were able to delete the private queues and reconfigure K2 to use private queues according to the following KB000198 (http://help.k2.com/kb000198). However, as of 4.6.9 we consolidated a few .config files, the SourceCode.EventBus.Server.Config file being one of them. We updated the K2HostServer.exe.config by configuring the line msmqpath="hSERVERNAME]EventBus" msmqerrorpath="hSERVERNAME]EventBus Error" as per the KB. This resolved the first part of the problem.

2. To resolve the second issue, we added a default SMTP connection string with no email address associated with it.

- Open the Connection string editor using an account with administrator database permissions (as the K2 service account, if at all possible)
- Click the green sign and select SMTP
- In the dialog box asking for the identity, leave the field blank and click "Ok"
- Select the newly-created SMTP connection string and fill in the details
- Click the Save button and restart the K2 service.