Thanks for reaching out about this, and great question. When emails encounter a firewall, if that firewall rejects the email outright, it would indeed show as a bounce. There are less common situations however, when the receiving server will initially accept the message --and before actually placing the email in the inbox, the message will encounter a secondary server filter or firewall. It sounds like this may have been the case for you, and if so, having your IT team take steps to update your SPF record should help the situation. I hope this helps! If you have any lingering questions about this, please let me know.