Hi @Madalina Roman ! Ebenezer here from Engineering Support.

After testing this for your use case, I found that building the series with one starting point with rules which splits into two will be a better flow for what you need -(in this example) having a post trigger for mobile users and a separate post trigger for desktop users.

For this example, we were able to get the post to trigger on the mobile device as you can see in the screenshot. Because the series splits for users on desktop devices and mobile device after the starting point, users cannot go down both pathways which will prevent the post from triggering in both cases. Once users go down one pathway (whichever type of device is detected first) they will complete the series and will not be able to go down the other pathway.

Hope this helps!

Hi Ebenezer! Thank you so much! Your example helps me identify some of the mechanics behind the settings.  

However, we still have some issues. 

Our need is to adjust the audience dynamically in the series  ( not spit at the beginning) - meaning that based on the device the receiver uses to open the email ( so if today 1 user opens on desktop, but tomorrow they’re opening on mobile, they need to see the email adjusted for mobile). 

So, just to clarify: we want to send two emails (emailA and emailB) to the same email list, but depending on the device they use, the email will be A from their mobile, and email B on their desktop.

Thanks so much and looking forward to your answer!