From the Marketo Email Use Policy:
"...You may not send any Unsolicited Email by use or means of the Marketo Service. "Unsolicited Email" is defined as email sent to persons other than: persons with whom you have an existing business relationship, OR (ii) persons who have consented to the receipt of such email, including publishing or providing their email address in a manner from which consent to receive email of the type transmitted may be reasonably implied."
The full text of the policy is here: http://www.marketo.com/trust/email-use-policy.php
An abuse report is a report that an individual sends to firstname.lastname@example.org alleging that a Marketo customer sent unsolicited email.
There are a number of reasons why someone might report abuse. Here are a few common reasons people report abuse to us:
For additional reference - Abuse Report Deep Dive