Blocked images
To keep email sizes down and increase deliverability, images in emails are hosted on our servers, instead of being sent with the email. Email clients refer to these as "remote" or "external" images, and may be set to display images in:

no emails
a specific email (as an exception if images are set not to display)
all emails from a specific or trusted sender, or
all emails
All desktop and webmail clients have settings like this, which might be applied based on personal preference, or controlled by a system administrator. In any case, it's not possible for you to override these settings, so your best strategy for dealing with image blocking is:

Keep your subscriber list well maintained and engaged with premium content they want to view.
Don't use emails based solely on images, include text as well.
Make sure all images have the alt attribute set.
Provide a web version link in the email.

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