what is the best way to set up a campaign for sending an email out to non opens? Do I need to have a trigger in the original email?
You don't need a trigger for this but an inactivity filter (Not Opened Email - see the snapshot below). You'd need to choose the correct email and any other constraint (if required). You can add this as a filter (along with other required filters, such as Marketability, Country, Segmentation, etc.), and in the flow, add the Send Email flow step to send out the email.
Just a note that opens/clicks are not 100% reliable metrics as they could be from bots/privacy scanners (especially if you don't have the bot filtering enabled in for your Marketo instance). Hope this is helpful. Please let us know if you have questions.
When I do this, it wants to send the email to everyone in our database who didn't open it, even though this email was sent to a specific list.
I will add another filter " Was Sent Email " , your criteria should be like this ,
Was Sent Email is X and Email and Not Opened Email is X , if you recently sent the email you can use Date of Activity in the past constraint as well