CSS closing .slot tags not recognized

Marketing Cloud Automations , Marketing Cloud Email Studio , Marketing Cloud Journey Builder , Marketing Cloud Sending

Last updated 2019-05-31 ·Reference W-5852877 ·Reported By 2 users

Fixed in version 219

Summary
It is possible for an email to fail validation when using CSS .slot tags within the email. The email will fail to send with the error "No closing tag was found for the Guide tag block. Guide tag blocks must be closed by a corresponding close tag of the same name."

Repro
Create an email which uses CSS with multiple opening and closing .slot tags in the email.

Workaround
1. Open the impacted email
2. Switch to the "Plain Text' tab
3. Click in the text editor
4. Click 'Edit' on the pop-up which asks if you want to edit the text only version
5. Verify that the text version is correct, making any potential changes that are needed
6. Attempt a test send

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