Ever had this happen to you? In gmail, this happens all the time. I’ve seen hotmail/outlook, however, let the same email through without issues. In either case, if you are the one getting an email and the following message appears — not much you can do (aside from opening the full message in new window).
But, if you are the one sending this email to your customers — listen up. Firstly, you shouldn’t be sending your customers emails, looking like this and I will explain why. It looks unprofessional, yes. You lose some of the content, that’s also obvious. You annoy anyone who already doesn’t like you even more, since the ‘unsubscribe’ button is no longer there. But that’s not all. Because the footer of the email is cut off, so is the code that comes with it that tells your beloved Mailchimp (or whatever you use) who opened the email and when. And not everyone clicks on “View entire message”. People are lazy, remember? And they also don’t care about you.
Now, how to not let this happen? Cut down your email content. And not just decrease your image size, that won’t do much, as images are just links (as in code). So what you need to lose is some extra code. That means any type-styling that you might have brought across when copying/pasting text. Or, you just have too much crap on that email of yours. Summarise and more importantly — send yourself a test message before sending it to the world and make sure everything is running smoothly.