Basically, you have an unique situation. To mitigate risk, invest in the resources to do thorough testing, i.e. set up a sandbox to sandbox replica of your current set up with a po...
Basically, seed your lists and check the inboxes which will let you know let you know to an extent if there's anything wrong with your emails. This is because spam filter settings ...
Please describe specifically the information you're after, "Handle" is a vague.e.g.Handling related to batch emails:If all duplicate records (matched by email address) are included...
Marketo's native behaviour upon form fill is upsert, but you can force create a record with a webhook to a handler that submits the lead data using REST API