Brightmail blocking Klaviyo messaging service

Hi there,

We're currently using the Klaviyo messaging service to send e-mails to our customers but we've noticed that our e-mails aren't sending to our customers which use the BrightMail spam filter. 

I have created a "email on acid" account (which allows e-mails to be tested against spam filters such as BrightMail) and done the following:

• Sent a preview message from Klaviyo of the message and it's current content and it's failed against the BrightMail filter.
• ​Sent a preview message from Klaviyo with just a blank body and it's failed against the BrightMail filter.
• Sent a preview message from another e-mail provider of the message and it's current content and it's passed the BrightMail filter.

Because of this I'm believing that the issue is with Klaviyo, however upon checking the sending service i.p (http://ipremoval.sms.symantec.com/lookup/) It doesn't appear to be black listed, would you be able to point us in the right direction? 

I've attached some images which may be useful.

Thank you very much for your time.