Hi @aggie_publicnectar ,

Welcome to the Community! Happy to help you troubleshoot this issue. 

This could be caused by a number of things, but let’s try to narrow it down by exploring a few settings!

The very first place I would recommend you check is the Klaviyo Email Editor for your campaign. You will notice at the top of the screen, that you are able to toggle between the Desktop and Mobile designs:

After selecting the Mobile view, do you still see the grey lines while in the Editor? If so, you may be able to click on those blocks and remove them, or hide them on mobile via the Display Options in the sidebar menu:

If you do not see the grey lines while viewing the campaign in the Editor, they could be appearing on mobile wherever you have padding/spacing between sections. If this is the case, the design will display the background color of the email, which you can check in the Styles tab:

By default, this is a grey color which is why I mention it as a possibility. Try changing the background color to another color that is easy to see (like a bright green or yellow) on both Desktop and Mobile, and send yourself another test email to see if that background color comes through. If it does, then you can change it to be either transparent, white, black, or another color that matches the email design. If the bright color does not come through in your test, then you can reset the background color to the original settings. 

If none of these settings work, it could be a result of the settings in the inbox provider you are testing this campaign in, instead of a setting on the Klaviyo end. Inbox providers, like Gmail and Yahoo, and even different device types (iPhone, Android, etc.) can also impact the way your campaign looks for the end user. 

There is a great thread on the Community here that discussed this variable further:

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Hope this helps!

- Ashley Ismailovski