Subject: Welcome to {account}, {first.name}!
Hi Sam,
Congrats on joining {account}! {account} is currently evaluating us (liasing with Sally and Bob) to see if there's a fit. As a (hopefully) happy ACME customer when you were at {previous.company}, can you share some feedback to them?
I've included the rundown below to jog your memory about ACME.
Let me know if there's anything I can assist and best of luck on your new role!