emails blocked as spam

According to the invalid email report @wavecable.com has blocked any email we try to send a customer with @wavecable as spam....

This is the message on the report "@wavecable.com said: [diagnosticCode] => smtp; 554 5.7.1 [VI-1] Message blocked due to spam content in the message."

How do we resolve this?

If the block is at wavecable.com, your question should be directed to them.