I have a simple list with one field I named ‘Recipient’. It is a name field that allows you to select other sharepoint users. The workflow has one action, send email that does a workflow lookup at the Recipient filed on the current item and returns the field as a semicolon delimited email address. When I create a new item and select myself as the recipient the email gets sent but if I select anyone else the workflow goes into suspend status with the following status:
I found that with in my 2013 farm with claims authentication I cannot set the Lookup for Person or Group – Return field as in the workflow context choice as anything but Login Name. Mine were also suspending with a 400 BadRequest, and I set variables and could see the email addresses, but no email would ever generate. In 2010 I had used email address or DisplayName and neither of those were working in 2013.