Hi Eric, Try this:
- Log in as a Sys Admin
- Click the Troubleshooting link on the left
- Click the Vew Logs card
- In the Delivery logs on the date this occurred, search for: Delivery for GMAILSENDER@gmail.com to
At the end of the log returned, you'll see: (Delivered) Filter:
If the filter says None, then no content filters were applied. If there's a name after 'Filter:', then that is the content filter being applied.