Learn in the textbookInternet Advertising (Billing and Placement Types)
DefinitionOpt-in email advertising (オプトインメール広告) sends ad emails only to people who agreed in advance to receive them.
ExplanationA typical setup has people pick the topics they care about when they sign up, then sends them ads on those topics. Because the mail goes to people who want it, it is more likely to be read than mail sent to everyone indiscriminately. Since its 2008 amendment, Japan's Act on Regulation of Transmission of Specified Electronic Mail (特定電子メール法) has also, as a rule, required the recipient's prior consent before advertising emails are sent.
AnalogyIt is like a shop asking, "May we send you news about new products?" and mailing the notice only to customers who said yes.
Memory hook"In" points inward: the audience is people who decided for themselves to step into the mailing list.