The hallmark of bad advice is the “there are very clear guideline” statement which appears without an actual reference to the “very clear guideline”. A great example of this is an Email Insider article entitled: “Transactional Email.”
CAN-SPAM. There are very clear guidelines on how much marketing content is acceptable in a transactional email (no more than 20%), and where in the email the marketing content can appear (below the fold).
There are, in fact, no very clear guidelines on how much marketing content renders a message no longer transactional. There is a rule of thumb (Matthew Vernhout, 2008), which may be widely used within the industry, and may even occasionally make a lot of sense, but this is not a “very clear guideline” in the context of what is (or is not) permissible under the statute.
Further, how do you even begin to give guidance on what is “above the fold” from a legal standpoint? “Above the fold” is an industry term that was stolen from newspapers to talk about content that is immediately visible. It means “in the first screenful of the preview pane” of a mail reader. But, what shows up there is greatly dependent upon the monitor size and the screen resolution of the recipient. If the marketing content cannot appear “above the fold” then does that mean it cannot appear above the fold for an 800×600 monitor, or for a 1280×1024 monitor? One of those “above the folds” shows more content than the other. Thus, if you plan for a grosser resolution (800×600) then people with finer resolutions (1280×1024) will show content that you thought was “below the fold.” Additionally, you run into problems of predicting the preview pane size and whether the program is running maximized (Jennifer Kyrnin, 2007).
For regulatory issues, demanding something with such high variability be planned for is a bad idea. It’s no wonder I can’t find any mention of this stuff in the statute, implementing rule, or caselaw.
Depending on this advice then, as your cover for stuffing marketing in a transactional email, is dubious at best. It’s best to consult your own attorney as to what the law allows, frowns upon, or forbids. Just because you read it on the Internet doesn’t make it so.