Receipt or order confirmation is not (or at least should not be)
a marketing e-mail. It's a technicality necessary for transaction.
Re:Ask HN: Plain text emails in 2017?
by notrheadagain on Wednesday August 30, 2017 @10:04AM
(#15132210)
However, the rule of thumb, especially for drip campaigns, is that you do get some marketing content with almost every email. This could be a specific sign off and such.
Regarding marketing emails, I mean every automated email sequence. Like, you definitely get receipts and stuff over email. And those aren't written by hand.