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How to Avoid the FISUE Syndrome
http://cdemails.com/articles/7223/1/How-to-Avoid-the-FISUE-Syndrome/Page1.html
Silverpop Systems Inc.
Silverpop is a leading provider of permission-based email marketing solutions, strategy and services.  
By Silverpop Systems Inc.
Published on 11/19/2009
 
I have an explanation for why people click the spam button on so-called "legitimate" email: the "Forgot I Signed Up for Email" (FISUE) Syndrome.

This often happens when people sign up for Webinars, free trials or buy something online. They either forgot they signed up or didn't realize that being added to your regular email program came with their transaction. You must make a clear case to your subscribers that your email is in their inboxes at their invitation. If not, FISUE Syndrome will claim another victim.