Dierdre,
I was able to dig into the bounces a little more closely. I also saw the 3 bounces with the following message:
"554 Spam violation, the content of your e-mail contains illegal characters, re-sent after examination"
This bounce was sent by the tom.com email network. This is a Chinese network and it is very likely that your email was blocked because it was in English instead of Chinese.
I hope this helps explain the bounce! Feel free to reach out to Support if you ever have any questions about interpreting these kinds of bounce responses.
Thank you,
Kiersti
Kiersti Esparza
Email Delivery Strategy & Compliance Manager | Marketo, Inc.