Hi @Brittany_Striew, I got an answer from Marketo support today as when Block Listed Cause is populated. It's a little long but I didn't want to remove the context leading up to the answer in the last paragraph:
"We manage our network to provide our customers with the highest server availability and best deliverability possible. Marketo Engage has a strong anti-spam policy and a team that handles blocklist notifications in our IP space and spam complaints. We also cooperate with most major anti-spam providers and ISPs. In addition, we maintain feedback loops for many of the most popular email providers.
Blocklistings are usually caused by sending mail to a spam trap email address. When we receive notification of a blocklisting, we react in two ways. First, we go through the procedures to remove the listing from that blocklist as soon as possible. Second, we determine (if possible) which of our customers caused the blocklisting and work with them to improve their mailing lists to prevent a reoccurrence in the future. This is usually a cooperative process, most frequently, a review of mailing policies and strategic pruning of a customer’s lead database will return them to best practices." [Reference]: https://nation.marketo.com/t5/knowledgebase/how-does-marketo-respond-to-blocklisting-and-spam-notifications/ta-p/248251 To Summarize the overly-wordy answer, as provided in the aforementioned documentation (URL Link Above): -- If Block Listed, Marketo's Security Team would reach out to you in an attempt to come to a mutual understanding, and get you back into following Best-Practices, to increase your chances of being removed from a Block List. -- If communication between Marketo's Security Team and the offending Account cannot be concluded, this is how / why / when Marketo would update the "Block Listed Cause" Value Field. (At least, until the offending User was removed from a Block List)."
... View more
A quick spot check also confirmed that these fields are not visible in SFDC to the Marketo sync user. I think that makes them safe for me to hide the ones not in use/no longer needed. Thanks again for the help!
... View more