I'm setting up an email trigger campaign, where when after someone fills out a form on a landing page they will start to receive a series of emails. I don't want to send email #2 to someone who opted out from email #1, so what's the best way to take opt-outs into consideration when setting up the flow steps of the campaign?
Marketo will never send a non-Operational email to someone who has unsubscribed. so there's no reason to remove the person just for the email.
However, if you would really like to remove such a person from the remaining flow steps, please place the Remove from Flow if Unsubscribed=T before the next email send. You can use this method with all sorts of conditions.
I usually Add to List before removing those people in case I need to track the drop off.
As long as the Unsubscribe field changes to TRUE when the lead fills out the unsubscribe form (which it should and is default behavior), the lead will not receive any more emails. You don't need to do anything else. Marketo handles this at the system level.
Removing unsubscribes from flow steps is still the case, right? In the light of the upcoming GDPR, that is a big deal.
You would have to explicitly remove from flow an Unsubscribed Lead. But the Lead will not get a non-operational email when it hits the Send Email flow step.