Hello @BreeL8 ,
This is unfortunately a widespread bug with Microsoft Outlook that affects all ESP emails, including those sent through our system. There are currently no legitimate workarounds for this issue, however, it only seems to affect certain Outlook versions. Microsoft is aware of the issue, and we're closely watching for fixes that are made available. If any are made available, we will take advantage of them. The primary issue is that the lines are random, so they could end up in different positions or disappear entirely with the next test or live sendout. That said, there are a couple potential workarounds you could try:
Changing the color of your inner background to match the outer background. This way if the lines still try to appear, they'll still be the exact same color and won't be seen.
Drag a divider or spacer block next to the affected block to create a column layout. Add all the affected blocks to one column. Delete the divider/spacer in the other column, so that the content is back to one column. We've seen this workaround have some success, but nothing is guaranteed due to the sporadic nature of the glitch.
For more info on common display issues in different email programs, such as with color and text formatting, I'd recommend taking a look at this post.
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