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Hi G, I wouldn't worry about it from an SEO point of view, changes of that size will have little or no impact. It's strange from a user point of view though to have the main heading of a page below the fold so I might consider doing it anyway.

No that should not be an issue...a single privately sent email to customers should not effect your rankings in the google rankings.  Do the due diligence on the provider company that you worked with, use the open site explorer and Webmaster Tools to see if you have new links, if so where did they come.  It sounds like an issue that is not related to the email...but at any rate try to find out why a dropped happened