We recently enabled safe links in our tenant. One of our faculty sends messages to hundreds of members of the faculty union. He uses Dadamail to send these messages. They all get delivered, but as soon as we turned on safe links and he sent a message: All subscribers immediately and automatically unsubscribed. He said it happened right after the message was sent. He re-subscribed everyone and tried a test with a smaller group. There were no issues. Then he sent the same message to a larger group and it again started to unsubscribe everyone, so it seems to be related to volume as well as to safe links.
Has anyone else encountered this problem? The messages are getting delivered, and the sender is not getting flagged or blocked in any way. Is it possible that the URL rewriting process is triggering the one-click unsubscribe script to run? Any thoughts on how I can verify this?