I have emails being sent with the email module that are being blocked by customers' Barracuda phishing rules. We're also a Barracuda customer. Any ideas on how to make emails less likely to be flagged?

Do you already have the email authentication records in place?

No, I was just using email.send().

You should look into email authentication. It requires some DNS settings and some generated keys/certificates which help the system assert that it is you sending the email. This should help you get past the spam filters.