The minimum requirement for constant inboxing is to use the best list possible. This can be done with double opt-in procedure the easiest way.
Many marketers feel, that Double opt-in slows them down. This is why:
A regular Double Opt-in will have a form, that sends an email, which opens a confirmation page. The visit on the confirmation page and the link will be checked by Mautic. If the condition for visit or click is true, then a campaign step sets the Double Opt-in value in the contact as yes. Something like this:

The problem here is, that the cron has to be used to create segment, push the contacts forward in the campaign, and also for executing campaign actions. As a result, you have to wait all the time:

The solution is to cut out all the ‘moving parts’ and perform the campaign actions right at the spots where they happen. The emails should be sent by the form, and the Double Opt-in should be set by at the confirmation page.
This way you have a simplified process:

The key is to assign the double opt-in verification tag at the confirmation page. You can do this many different ways, via PHP + tracking image, Javascript, or WordPress slug. I have a video explaining and testing all three of them:
As usual you can download the scripts in your Download Center, which is available after login, or free registration.
Hi,
Need to know what “set by” means here: “The emails should be sent by the form, and the Double Opt-in should be set by at the confirmation page.”
It means you could add a tag to record the page visit. You can do this by adding tag value to the tracking pixel.