Emails in a K2 workflow stopped working after deploying new workflow version.

The workflow fails while trying to send a notification with the error "SourceCode.Workflow.Common.EWS: The e-mail address does not have ‘send on behalf of’ permissions on Exchange".

1. Check if SMTP server, Exchange server connection strings are correct in “ConnectionStringEditor.exe”
2. Open Connection String editor from "C:\Program Files (x86)\K2 blackpearl\Host Server\Bin" as Administrator.

3. Check if Email "From Address" field value is a valid email in Environment Fields/String Table and same as the email displayed in the connection String editor.
4. Restart IIS, MSMQ and K2 services.