Hi Macarena,
On email, you would you media queries to hide and show content based on the device. It would not work everywhere, though. Typically, only the most recent versions of Android devices support media queries. In any case, it will take a developper and Marketo Dynamic content would not help.
On LP, you can do this if you create a segmentation by device and rerender the page, passing the segmentation as a URL parameter. I'll let Sanford Whiteman provide more details, he is the true Guru on this 
-Greg
You ware welcome.
It's important to note that on email:
- You cannot use Javascript in an email (at least if you do not want your email to be considered as a Virus )
- You never know in advance on which device the addressee will open the email and you cannot interact with the Marketo server once you know
- So if you want to change the content based on the device, it has to occur on the email client
- So the only method left is CSS/media queries, which are not supported on every email client.
An alternative would be to presuppose for each person what device they are using, based on previous email opens, and create a segmentation on this. There are various possibilities to do this. See Josh's article below.
-Greg
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