Are there any related issues?

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No

What operating system are you using?

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Windows 10

What version of Mailspring are you using?

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Dev build (1.06). Issue persistent in Stable builds as well.

Bug?

Do you have any third-party plugins installed? If so, which ones?

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With no plugins installed, picture of Youtube video in the email is completely blank. It will open, though

Is the issue related to a specific email provider (Gmail, Exchange, etc.)?

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No

Is the issue reproducible with a particular attachment, message, signature, etc?

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Yes

Feature Request?

Does this feature exist in another mail client or tool you use?

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Web Gmail