We've noticed over the past month or so that our email deliverability has gone way down! I asked my Customer Success Team, but they just provided me with a link to Pardot's website which had the email bounce codes listed. I still would like to know if our IP address has been blacklisted anywhere. Is there a way to see this? How do you know what your IP address is? I can't seem to find it in Marketo (I've looked in email settings as well as the Admin email section).
I'd also suggest looking on the causes for bounces or email invalids. The code numbers by themselves won't mean much but the email invalid reasons/hard bounce reasons will give you some insight into why this is occurring.
Over a year ago we experienced a huge drop in deliverability and it so happened that our Marketo IP had been flagged for spam from another client's email activities and it showed up in the email invalid/bounced reasons.