Images appears as broken in newsletter email

Hi creverter,

First of all, thanks for your work, this plugin is awesome!

But I’m having a problem since two months ago. I’m using the Casablanca template for newsletters and for any strange reason, the images that I put on the newsletters don’t appear when subscribers receive them. Even the icons in the social module. This error doesn’t occur in previous newsletter, and if I resend it all appears to be ok. If I press the “Can’t read” link on the problematic newsletter mail, the newsletter is ok

Please, could you give me some light about how to solve this problem?

Thanks in advance