What you are referring to is called Preview Text, this article from Litmus tells you all about it and how to fix: The Ultimate Guide to Preview Text Support - Litmus Blog.
Don't worry too much, even Marketo has this issue:
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This has to be done in your template and your email. The very first line of your email should not be the "view as web page" text and link, but something relevant to the reader and complementary to the subject. The template has to accommodate the editable section for this.
We'll have support for this in the new email editor! Hopefully then our marketing emails will look good too!
We just add an element in our templates for 'pre-header text'. This way you can populate that so that you can tailor the message to the people who will see the pre-header text, but it doesn't have to show up in your email anywhere that is actually visible to the viewer.