I have applied for many jobs on many systems.I notice on some that they let you see if your reference responded to the auto email. One of my references always responds the same day. Another, the teacher I student taught with, just ignores most emails. When I worked in her class she literally ignored email and/or got really overwhelmed by mail and started deleting weeks later. But alas, she is my only classroom reference.This summer I made sure to send thank you cards to her, my principal and the university supervisor, just in case they don't feel like doing this. Can this get in the way, in your experience?