The simplest way to do this is to include your logo front and center at the top of your email header.

http://beehive.instructure.com/eportfolios/4684/Distaclor_Cd_Production_Companies__Invida__Antibiotics
http://erau.instructure.com/eportfolios/70102/Gp_Test_U_Cj_Levels__Geneza_Pharmaceuticals__Injectable_Steroids

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Having said that, there s a lot more that they could be doing to ensure that no spread happens.