What you can to, if your workflow don't work.

To see, what was happen during one execution, you could use the Statistic Tool. This tool show the way records take in this workflow.

If an eMail won't be send, you could see a detailed SMTP Log in every Mail task, which was entered in Statistics view.
To get this, 1. click on a path in the workflow, which the record you want to check has taken, before the problem.
This will open a list with all records, which had taken this path, in the left sidebar. (If there are many record, this could load some seconds)

To view a single record, click on the » next to the record, you want to check. This will show how the record walk through the workflow.
If you now double click on a block, you could see additional information for this single execution of this block.
In case of sendmail, you see the complete SMTP Log.

Also you could configure an mail Address, which will receive error messages, which happen during executions.
This could be done in the “Log Management” settings page on Workflow Designer overview.