Symptoms

We found some times Mail Event occurred error. Our SMTP is from smtp.office365.com

How to find the root cause and how to prevent this error.

Here is error log from host Server
"6606228","2016-01-20 15:30:34","Error","General","0","ErrorMessage","SourceCode.Workflow.Common.SmtpMail","0 SMTP mail send failure: Verify the SMTP connection strings are correct and that SMTP is working properly. Exception: The operation has timed out.","anonymous","0.0.0.0","DLX:C:Program Files (x86)K2 blackpearlHost ServerBin"

"6606229","2016-01-19 21:16:21","Error","General","28083","ExtenderExecuteError","ProcessInstance.HandleException","28083 ServerEvent: There is no connection string for the destination email address workflow@xxx.com.
InnerException: There is no connection string for the destination email address workflow@xxx.com.","","","DLX:C:Program Files (x86)K2 blackpearlHost ServerBin"

 

Diagnoses

Since user is currently using Office 365, user can switch over to use Exchange for your email notifications.
 

Resolution

1. Performed reconfiguration of K2 to use Exchange instead of SMTP
2. Used connection string editor to check if EWS connection strings are configured correctly
3. Modified the Exchange Server and Mail Server Environment Library fields in K2 Workspace