Symptoms

We use out of the box smart actions on email notifications such as Replying with "Approve" for managers. Previously if they typed a response they would get an email that the Approve Action was successful and the process would continue to the next activity or task. Now it's not working on several apps so it seems it must be a configuration issue. Nothing has changed except K2 did help us fix a cert configuration issue. But I'm not sure it happened exactly after that. The apps were republished several times since then
 

Diagnoses

Reviewing K2HostServer.exe.config file, we noticed that SmartAction is disabled.
 

Resolution

We run the ConnectionStringEditor.exe from oInstall Dir]K2 blackpearlHost ServerBin, and make note of account that the account configured for SmartAction. We modified the K2HostServer.exe.config as follow, restart K2 Service, and that resolved the issue.