Blocking would not surprise me, our corporate IT did not originally want to whitelist Workfront or Proof because of the over-broad way it must be done and vulnerability to spoofing. Every time our IT updates their spam filters, or add another security layer, Workfront and Proof get caught in the crossfire.
As Kyna said, you'll need to double-check the receiver has the proper whitelisting set-up. The receiver's IT should have logs of what they have blocked or quarantined, and Workfront Support can check email logs of sent emails. Took a little detective work, but we've been through this twice now and gotten it straightened out.
