Like promotional e-mail, transactional e-mail by nature bypasses search engines.
Uh? What? My car also by nature bypasses search engines (although it does, in fact, have an engine of its own, thus providing at least as much linkage to search engines as transactional email has).
Maria Krueger is a Web Analytics Specialist at Skyline Technologies, Inc. Or, so says the article and I suppose that explains why the article talks about email and search engines.
Also, in this article we have this quote (which is what drew my attention to this article in the first place):
Transactional e-mail does not have CAN-SPAM requirements, such as an advertisement notation at the op of the e-mail, a U.S. Postal Service address, and an unsubscribe link.
Well, that’s not exactly true. Transactional email does have some CAN-SPAM Act requirements. Namely, Section 5(a)(1) prohibits materially false or misleading header information and mentions transactional and relationship messages specifically as being covered.