Simple workflow to change date in related field


I’m new to the SuiteCRM world and am trying to set up what I think should be a fairly simple workflow.

In short, I’ve added a field to the target module called "Last Emailed’ The idea for the workflow is that each time an email is sent it updates the Last Emailed field in the relevant target record, so that I can see easily at a glance who has been emailed recently. I’ve attached a screenshot of the workflow I built which I think should be doing the trick, but something is not working right. Each time an email is sent the workflow registers as having run but does not update the appropriate field.

Any help you can provide would be greatly appreciated – and maybe there’s a better non-workflow way to do this?

Thanks for your help,