Hello, Litmus community! Has anyone noticed that HTML emails in Mac Outlook always have an unwanted space on the left-hand side?

Even Litmus's own marketing emails have this defect:

I've tried everything, even building an email that was nothing but a table with a background color set to width 100%, but this space always appears.

Is this a known issue? I could not find anything online about it. Any solutions?

I know Microsoft has pledged to fix Outlook, but since it took them 9 years just to acknowledge they've made email development a living hell, I'm not holding my breath!

Thanks, all!