Hi all,
I'm on Marketo's Privacy team. We handle email deliverability and compliance issues.
What Josh is describing is called a role based address. A role based address address is something like a support@, admin@, or info@ address that is meant to be an alias for people belonging to a group. These are dangerous to mail to because most people do not sign up role based addresses for commercial emails, so having a number of them in your list may be a sign that your list members are not opted-in to receive emails as they should be. Sending to role based addresses can also increase your risk of feedback loop complaints, because sending to one info@ address that goes to 5 different people increases the chance that someone will complain by 5. Hope that makes sense.
What Daschel is asking about is spam trap addresses. Because spam traps are proprietary to the blacklists that own them, you cannot know what addresses in your lists are spam traps. Marketo can't determine this for you either. This is why they are a little trickier to target and remove from your database. Below is an explanation of what a spam trap address is:
https://community.marketo.com/MarketoArticle?id=kA050000000L3Ex&src=
The best way to clear your database of spam trap addresses is to clear out your inactive leads. Many people clear out their inactive leads every 6 months or so. An inactive lead is a contact that has taken no action in the given time period— they haven't opened an email, clicked a link, visited your webpage, attended a webinar, etc. Inactive leads are a dangerous group to continue mailing to because they might be spamtrap addresses. They might also just be people in your list that do not want to interact with your mail, and are therefore much more likely to log complaints against you with their ISPs.
You can find instructions on how to remove inactive leads at the link below (about halfway down the page):
http://community.marketo.com/MarketoResource?id=kA650000000GtqlCAC
Hope this helps!