Thanks for the reply.
The DFP behaviour is to download a file.
I've found that if I move the UE behaviour above the DFP behaviour and change the trigger to "Send if recordset is not empty" then it sends OK. So some success there.
In the trigger events list however there are two that say "download 1 successful" and "download 1 failed" I really only want to send the email if the download is successful. I know the recordset won't be empty. So in other words the email is currently sent whether the file is actually successfully downloaded or not. Defeats the object really.
I've tried using the trigger of download successful but again it's not sent.
Neither behaviours have a redirection in them.
However if there is no other solution I'll live with what I've got.
Many thanks for pointing me in the right direction.